Google is always listening: Live Test
youtube.com
youtube.com
So it's either a weird coincidence or _someone_ is listening. How and who is still unclear, until the experiment is repeated in a more rigorous manner.
My hypothesis is Google running some text-to-speech from the stream, as any other form of local spying would be visible in network traces, whereas you're sending your stream to Google servers and what happens there is opaque.
Many people, me included, have seen ads after talking about a topic for the first time. My mates got Bitcoin ads just after I've spent most of an evening explaining what it was to them for the first time.
It might be the Baader-Meinhof phenomenon in play, or someone's actually listening. It's definitely something we need to explore.
EDIT: how has this dropped from the front page so quickly?
1. You most likely have had thousands of cases when you talked to people about something and they didn't get an ad for the topic afterwards. One care hardly proves anything.
2. In Bitcoin's case, it's even more likely that this would happen coincidentally, since it was a temporary fad that got popular over a short period of time, during which time you had an increased likelihood of explaining Bitcoin to your friends, and your friends had an increased likelihood of being served Bitcoin ads, even independent from each other.
So 2 ads for dog things before he clicked on one, seems a pretty extraordinary coincidence
One thing that wasn't clear was he closed Chrome before he started discussing the dog toys, so how was google supposed to be listening? Unless it was via a different device e.g. an android phone
EDIT: Someone in that reddit thread said something interesting though, the guy was streaming directly to YouTube so it could be plausible that Google was listening to the stream audio and using that to feed into his targeting profile