Why did he add my house mate?

[Anatomy]

After going back to a guys house after a night out (I'm 20, calm it) we proceeded to sort of stay in touch. He followed me on twitter and would message every now and again about meeting up which I've always rejected due to not being able to at that time etc not through not wanting to. The night we met, he also met one of my house mates and though he didn't follow her until she followed him on twitter and they've never spoken to each other, she's just informed me that he's added her on facebook (he hasn't added me on facebook). What is that all about? Should I say anything?

[Thad]

Just be cool, it means nothing. He probably doesn't know you have a facebook.

[Ryan]

duno