Well, he was coming off getting to the US Open jrs Finals, where he beat the #1 seed along the way, IIRC, wasnt it Tomic that he beat???
Then he gets to the Wimby jrs semis, plus the Roehampton semis also, I think. Maybe he felt going back to college would have been a step back.
He's won matches at the Futures level before turning pro, I'm sure he felt he would continue to win, and more frequently. Maybe he's having trouble with the pressure. He played Haas and Federer tough, plus close losses pretty much whenever he's competed in a tour event, MD or qualies, that has to be encouraging.
He did beat Tomic, though Tomic was actually the second seed behind Yang. He also beat Krajinovic before losing to Grigor Dimitrov in the final.
As for Roehampton, he won that without dropping a set I believe.