The big question is why did this topic come up "out of nowhere"?

And there can be several reasons!

1. You unconsciously saw an ad for it (could even be a billboard while driving) and that's why you started to discuss this topic. If it's a new ad it now also pops up on your phone (as it's a marketing campaign) and you immediately recognize it because you've seen it before and discussed it

2. The ad campaign has been running for ages, but you never paid attention to it. Now that you discussed this topic with a friend you suddenly noticed the ad. Nothing changed ads wise, you just never paid attention to the topic

3. It's a popular topic in general, could be in the news, could be hip at the moment, for some reason you and your friend started to talk about it, where did it come from?

There's so many ways this can go. And if we go back to tracking: All it takes is for a friend of yours to later search something related and it's also hard tracked (and then linked back to you as you hung out with them). Which can be a double whammy. Your phone being "ungoogled" is also worthless if you use Google, Facebook, Instagram or whatever.