It's technically possible but very unlikely. Running TTS continuously is a big battery drain and slows down the rest of the phone while you're using it. Google has a live TTS service for hearing impaired which I've run for a while to test it, and even with it practically built into the OS it's sucking up battery like you'd expect it to.

It's more likely that this is all due to external forces. Having your device on the same network, in close enough proximity to detect each other, for instance, combined with one of your friends having Googled the stuff you were talking about.

Or just basic data collection. There's the classic story about how supermarkets know you're pregnant before you do, just based on the groceries you buy (no, not pregnancy tests). Ad networks buy and collect a humongous amount of information about everyone and serve ultra specific targeted ads based on nothing more than pattern matching based on what the rest of humanity is doing.

It's impossible to rule out that the thing did run a 24/7 TTS service, but I think the depressing fact that ad networks don't need to listen to our conversations to know what we're talking about is more probable.