It's becoming a real concern for normal people - they don't understand what it is or how it works but they really don't like it.
I was in shock when I saw it on Instagram on my brand new iPhone (switched from Android) which has all mic permissions off by default. So some 'smart' device in their home must of heard us. Some advertiser somewhere must have my voice profile hooked up to my Instagram account by now and they somehow share it in an "unidentified" way.
Edit: We need further research into these 'impossible' ads to see if devices from different software OS' and companies are listening and grabbing detail and showing ads based on what are supposed to be 100% private conversations.
You might have not googled it yourself, but I bet the person you had that conversation with did. If the conversation took place in real life, then that person's device was in physical proximity to yours (i.e., location data tracking; for example, if you enter a room full of people who googled tons of stuff about a certain subject, expect to see ads around that subject popping up on your device in the near future, even if you didn't google anything about that subject before and aren't planning to do so in the future). You also probably exchanged contacts and called (or texted) each other about other stuff in general (probable, but not necessary for the scenario I am describing). And if the conversation took place online, then it is even easier. Here you go, you just created a social link between yourself and the person who googled stuff about aircraft hangar gravel. In which case, it isn't surprising at all that you got that ad.
So in a sense, you are correct, it wasn't a coincidence. But I heavily doubt it has anything to do with smart devices listening and analyzing to what you said at all. It is much more trivial and less creepy to simply utilize your social links to figure out what kind of ads to display to you than listen in and try to analyze your conversations. More reliable too.
Facebook literally knows who your friends are. If your friend is interested in something there’s a good chance you are too.
Maybe not all of us, but for me it's an important and differentiating feature.
What we don't really care about is hypothetical thinking about wether we care from people that apparently don't care.
I don't think they know each setting that is available, but they without doubt have the impression that "Apple is better with privacy"
Do you think iPhone users care that Apple is implementing anti-tracking?