It's out and out theft.
Calling AppleCare - Apple's customer support - apparently? No, it is not reasonable. Going above and beyond the call of duty would have been stuff like - leaving contact information at the bar, so if someone comes looking for it they can get in touch with you; calling Apple corporate (you can find the number on apple.com/contact ) and demanding to speak with someone in charge; having access to the guy's Facebook information, you can try contacting him directly; and so on and so forth.
The "finder's" actions are a lousy cop out, after which they started shopping the phone around to tech blogs.
EDIT: Im sorry, why is this not a good idea? Clearly calling Apple care is going to be pointless if you have a secret prototype in your hand. Going to the management seems logical.