It's probably made-up garbage. If they knew my ad-blocker had actually blocked a friend, I'm sure they would have found a way not to get anything blocked.
Or alternatively they are now displaying some friend's posts on the same channel normally reserved for ad networks so they are indistinguishable via software? But then it should be way more than one, unless this is some early A/B testing crap.
I saw sometimes ads that was claiming that one of my friends like that product too. My bet is on that.
BTW: I started using user script to remove recommendations, suggestions and other crap like that. It makes Facebook so much more bearable but interestingly also feels less addictive.
After installing it, you will see a floating icon on bottom left, where you can configure it to filter more (I think by my or only blocks clear ads, some people might like the suggestions, but imo they are there to keep you engaged, so I would block them too).
Since user posts aren't ads, yes! But wouldn't be surprised if on their end what appears to be normal user posts (and are) are served through the ad system, so that it actually works that way.