The Baby keeps staring at him... Why?

So as completely random as this is, I have a 7 month year old baby boy, and he's just the best baby you could ask for... It makes sense that he's going through that phase where he's trying to observe everything, so he's always moving his head, and looking around... It's very hard to keep his attention, for even a short amount of time, but that's not the problem. In fact, this isn't even a problem, but just a mere random question. My sister has a boyfriend, age 17, and there could be many people in a room, and something loud and bright going on, but no matter what, the baby is always staring at her boyfriend. He stares long enough, to where everyone has noticed his obsession with him, and we've tried letting him hold the baby, and even then, he just looks right up at him with wide eyes... Could there maybe be something about him, that seems to deter the baby's attention away from everything? I mean, he's a fairly normal looking kid... But the baby never fails from staring at him...