For him it's normal, for you it's not. Why are you even looking at his Facebook page? Is he showing it to you, along with the pics? Or just another he left it on the screen and I happened to wander by moments?
My wife has been on Facebook for a couple of years, I've never read anything she's ever posted or that was posted on her page. I don't know anything about it, and don't have a Facebook page. Like you said, you don't care, he's with you, not them. It's normal for some people, your boyfriend for example. Just let it be. If he wanted to leave you and be with someone else, he can. He wasn't sentenced to be with you.
Be yourself, let him be himself and enjoy life.
...as ancient astronaut theorists would suggest