No, it's due to illegal SEO practices where they serve Googlebot a plate of GPT3 meets keyword spam, and then serve you a page full of advertising and phishing links.

I've been wondering for a long time what's been going on. This makes a lot of sense!

So if the User Agent is Google, the website produces relevant-sounding content with no JavaScript spam? I never realized GPT-3 could be used for this. The next time I see a bait-and-switch website in my search, I'll try changing my User Agent to Google.

GPT3-alike, not GPT3 specifically. Google’s bot can’t detect when it’s being fed plausible gibberish, or worse, stolen content with random keywords injected. I’m very curious if your Googlebot surfing comes up with any interesting outcomes!

I wonder if Google indexes with browser user agents sometimes: unless the site used source IP tricks, it’d let Google detect this sort of thing.

Supposedly the Chrome safe browsing service crawls the web looking for malware. Since that's focused on finding malware they likely make it look like a normal user in terms of user agent and IP address, so it can probably detect these pages.

I believe the signals from the safe browsing service are used to affect search result ranking, but I have no idea if they look for different content being served to the Google crawler.