He may have been staring at you nonstop without any facial expression and with his hands in his pockets because he was trying to gauge how you would react to him in the hopes of not giving away any signs that he likes you as well.
At this time, he may be wondering if what he has heard about you liking him is actually true.
He may have been staring at you because he wanted to see for himself if you would respond in any significant way that would allow him to truly determine that you like him.
He kept his face expressionless and his hands in his pockets because he wanted to be as neutral as possible.
He didn’t want to give away any signs through his facial or overall body language that he likes you back. He just wanted to observe without influencing the moment in any way.