The guy lacks communication skills and common courtesy, but unles paper was signed, nothing legal prevented him from taking a better deal if he found one, which it sounds like he did (Guy: "Sorry, I've already got somebody else to do it." Other Guy:"How much are they doing it for?" Guy:"$XYZ." Other Guy:"Oh, WE'LL do it for $XYZ - $ABC!" Guy;"Well, I'm sure they'll understand. You got it." OR... Guy:" Hey - I've heard of you. You packed 'em out at Club Drixxle last week. We don't have anybody booked yet. It's yours! Glad you called before anybody else did!")
Happens ALL the time. Sad but true. Your "real world" options are to either get back in touch with him and undercut the other band, which is a REALLY slimy thing to do, but is also something that happens all the time (although it's a practice I refuse to participate in even though it's cost me more than a few gigs) or else file this guy under "Can't Trust Him Any Further Than You Can Throw His House", and do business with him accordingly in the future.
I'd suggest the latter, because in THIS business, with communication skills and personal ethics like this, this guy's BOUND to hit it big pretty soon!