Guys who sabotage their college careers for the NBA usually do it one of two ways (or both) - being overly ball dominant or trying to show a skill (ie three-point shooting/ball handling) that would fit their NBA career instead of playing the way that would most help their college team. Rudy did neither. You could fairly argue that he might have been a really good stretch 4 in college, but with no 2 guards and a frontline that had Boone, Armstrong, Adrien and Nelson, he needed to play the 3 here.
Saying he wasn't passionate enough because he was worried about the NBA seems like a conclusion in search of evidence. He didn't have to come back as a sophomore, and reportedly he did wrestle with coming back as a junior before JC more or less told him that he was ready and needed to go. That could be just the story they told the media, and maybe Rudy had no intention of coming back, but I'm not sure who would have gained from that. And JC sure didn't think his 2006-07 team was going to be better without him - that was his second worst team behind the Economou/Besselink bunch he started out with.