I'm willing to give the homeless guy a little credit for being intelligent enough to know that his actions may very well lead to sincere job offers - good publicity and all that. Worth a hell of a lot more than a few grand.
I also think he was expressing some very well-meant contempt for the "I am proving that I care" self-congratulatory condescension that is a big part of most people's motivation in giving to social media causes like this. He is instead throwing the real issue up high in the air for all to see, that the problem is so much more vast and desperate than just him.
TLDR; I think he has too much respect for other homeless people to sell out and take the money.