[hellweaver666]

I know FB have a lot of really smart data-scientists working on this stuff but I doubt that it's worth the effort to analyse everything you say on the hope it'll contain some kind of keyword that can trigger an advert.

It's more likely that you and the friends posted pictures at around the same place/time your friend later googled micro projectors and was tagged via an embedded like button on the page (yeah... those things track you!). Then they just made a jump that two people in the same area may have similar interests and served you an ad.

It's just like how I get recommendations for people I've never met before after attending an event that we both just happened to go to.