Re: aaahhh facebook, i love you so!
And why Facebook's invested quite a bit into uncovering fake stuff. Just because YOU post fake stuff doesn't mean some of your friends (who use Facebook but you don't know that) can figure you out. Even if you never use Facebook at all, you probably have a pretty robust profile based on the info of friends who use Facebook but you don't know it, so that people who want to get you can plunder that information without your knowledge. It can get really scary, and the worst part is that NONE of this stuff is under your control. It's basically stuff stitched together from your encounters with others: necessary evils for functioning in society, period.
Oh, and let's not get started with the stuff that the government knows about you (and you're obligated by law to keep current) and posts publicly for all and sundry to see.