OK I THINK WE SHOULD TALK ABOUT THIS.
At first, Sam was sitting on the desk that near the window. And when Dean took out the laptop he was superised, ‘cause Dean is not the one who usually do the research, and it’s seem to me that Sam was kind of piss off owing to the distance between them. It’s obviously Sam felt uncomfortable about this situation, but for some reasons (maybe ‘cause he is the one who said they’d better keep some distance to each other), he just turned back.
But soon at the next scene, Sam was sitting opposite Dean! Which means Sam moved to there, only because he couldn’t bear that distance between them.
It’s really hard to leave someone when you were really close in your whole life. Not matter how he piss you off.
Well at least this makes sense to me.