I was at the game too, I didn't boo, because I don't boo. However, during introductions, he got a rousing ovation, which is cool, his teammates were jabbing him about it.
During intros, he's a former Sooner, during the game, he's a Clipper. I don't think he got booed. I think he just got treated like an opponent. When he's at the line, you cheer loud so he'll miss. When he misses a dunk, you cheer. When he makes an amazing play, you ooh and ah, but you don't stand up and cheer. As a Thunder fan, you're rooting for the Thunder. These guys are professionals now, it doesn't matter where they went to school or if they went to school. I'm as big of a Blake fan and an OU fan as anyone, but I cheered for Kevin Durant tonight.
Maybe it's easy for me. Growing up an Astros and Oilers/Titans fan, I've been forced to cheer for the likes of Roger Clemens and Earl Campbell and Vince Young. It's no big deal.
As for cheering for Mason, he was cheered for being a former Thunder player, just as much as being an Aggie.
This is sports, we can't take it that seriously.