This isn’t evidence. Even if Facebook was not listening to your conversations, there would be some rate in which you would just randomly be served an ad related to a topic you were discussing. There needs to be evidence that it is happening at a rate too high to be attributable to chance.
Sounds like a good way to engineer it... anything to improve the bottom line even if insanely-targeted ads only trickle out to users. How about limiting who sees this feature to also limit the risk of being detected? Maybe just do it once a year to everyone, or never to specific "tech-savvy" users that they have completely profiled.
