Likely a cognitive bias there, we pay selective attention to the topics we've been discussing previously, and likely remember when an ad comes up that's related. So yes, they're not listening to our microphones. It's just our selective attention and memory, instead.
The scarier reality to me is less that I'm being actively spied on and more that we're all very algorithmically predictable. Why bother actively spying when it turns out that the websites they visit in a day does a good enough of a job predicting what kind of person they are.
