Note I hadn't clicked the link yet, simply read the small paragraph my friend wrote along with the YT link "hey check this guy out he is using autocad for blah blah".
That was the day I stopped using Gmail.
Me and my friend have an interest in model aircrafts and drones and often spoke in person about building a new drone/airplane from scratch as fun project and this was the first time that Autocad was even mentioned in our discussion. Another data point we are both old school and would talk about this over beers in the pub rather than through messaging apps.
The only thing linking me to Autocad was that single email I got in Gmail.
I'm sure you can come up with reasons this is not breaking T&C but it would have never happened if the two products were in separate companies.
And I'm sure they will "not use" the health data in a similar fashion.
Additionally I wouldn't find it weird for calendar or maps to make suggestions based on gmail. That is the value proposition by adopting the Google ecosystem.
Of course, you could just as easily conclude that they're lying, but I find that harder to believe.
Everyone has some stories about how Google drew a suspicious correlation between products not supposed to be connected. In my case, there was one day where I wanted to watch an MP4 copy of Harry Potter I had on my NAS while on a work trip. Obtained ages ago. I uploaded it to my G-Suite Business Google Drive (not shared, nothing was pirated here despite ripping blurays still being a legal ish-zone). Later that day, YouTube started suggesting clips from Harry Potter to me.
Suspicious. Not damning. Are they scanning my Google Drive for filenames to feed to the YouTube recommendation engine? I don't know. Maybe it was just chance, or maybe a few days ago I clicked on a random article about JK Rowling's latest drama and that was enough to trigger three layers of indirection through the Google Brain and suddenly I love Harry Potter (I don't. Its fine. I'm sure after writing this out, though, Google's opinion on My opinion of it will be reinforced.)
But lets say I never watched those videos recommended to me. Is the YouTube recommendation engine data fed to their ad engine? What if I never click on something, but the system knows it presented it, and maybe I like Harry Potter anyway? I don't know. But it seems feasible, doesn't it? And if that's the case, then the data traveled two steps, where each step on its own is weird, but reasonably ok, but the two steps together look less ok.
We're really talking about the absolute cutting edge here; Google is building a brain processing exabytes of data. If you're in engineering; have you ever worked in a job where you felt like you knew how every part of the system worked? I work at a company with 10 people and I still don't feel that. Why would Google be any different? Teams talk to other teams. A middle manager two jumps up approves it. They get access to a database. Data travels around. An engineering lead at the top thinks they have a grasp on everything, a grasp spuriously assembled from reports written by people who themselves understand some non-100 percent of whats going on in their silo. Things fall through the cracks, it happens all the time, and in this case we're talking about buses of data so big that no one could even look at it all to verify what's in there is what they think is in there (and if they did actually have humans look at it, that'd have concerns on its own).
This is my pet theory: That the desires and realities of Google are so different that even what they say is untrustworthy because no one there knows whats actually going on anymore.
Regarding the spooky coincidence effect: the truth is that people are a lot more predictable than they assume they are. More often than not, when you're doing a thing related to X and then 10 minutes later you see an X ad, it's because you're actually in the bucket of people who like X and the buckets are highly correlative. You might be in that bucket because you like Y and 95% of people who like Y like X, and a search for Y, followed by doing something related to X, triggered the X ad because of the Y search. There's also huge confirmation bias on those coincidence ad views; everyone has a story of one, but I've yet to meet anyone who said "I sat down and recorded every ad I was shown for a week. 90% of them correlated with an activity I was doing in an unrelated Google product between 5 and 10 minutes before the ad was shown."
I can absolutely see this happening due to their sheer size losing control as everything is probably silo'd and confusing.
Due to a tax issue last year, I urgently needed a specific from a former GIANT company I worked for per my accountant.
It took over 6 days of calling, emailing and getting transferred around the bureaucracy because they had recently outsourced that HR function to another company and moved all the data and the Director of HR for that entire 1000 person department couldn't even get me the form and didn't know what to do! She and I had to put in a ticket together to the help desk and eventually someone at the outsourced help desk escalated it enough that we found out the physical forms were actually in transit to the east bay offsite location and had not been digitized yet which is why they were not able to provide the form until a 14-business day turnaround.
It was the most absurd and frustrating experience and definitely made me happy I'd moved to a more midsized org. We might not be an industry Titan but at least are small enough to be functional and not get entirely lost in bureaucracy.
It's not impossible that that would happen, but it would be a departure from current behavior. To some degree, Google is selective about what data does and doesn't feed into ad targeting.
Examples:
(1) Emails are sensitive, and Gmail messages are off limits: "Google does not use keywords or messages in your inbox to show you ads. Nobody reads your email in order to show you ads." (https://safety.google/privacy/ads-and-data/)
(2) Drive/Docs/Sheets/Slides (if I'm interpreting this right): "We will not use your content for marketing or promotional campaigns." (https://www.google.com/drive/terms-of-service/)
And they've already stated they don't use health data: "We do not show ads based on sensitive information or interests, such as those based on race, religion, sexual orientation, health, or sensitive financial categories." (https://support.google.com/admanager/answer/140378)
It is very reasonable to ask how your data might be used or misused. But the scenario here supposes that Google will change its general pattern of behavior and go against what it publicly said.