in the car/bike repair business it is possible to have a lien placed against a vehicle that has had repairs done, or more commonly been in an accident where the owner has no insurance and they just never come got it ... it's legal to sell it for salvage.
normally it's stated on the repair order you sign before most reputable service people will ever touch your vehicle..
I could find the exact wording if you want.. but in essence it says if you don't pay, or make payment arrangements in X number of days we reserve the right to sell your vehicle and apply the monies collected to your debt. If it total is more than your debt your supposed to get the rest of it... but most people only ask whatever the bill is for to sell it to junk yards really quick. no title needed.. just a reciept.. for example..
I just sold a 92 4x4 jeep that had been flipped into a ditch by a drunk man with only liability insurance.. the wrecker bill was $550.. he never showed up.. tried to contact him several times and he just blew us off so we sold the jeep (probably totalled anyway) to a salvage yard for the amount of the wrecker bill.. credit the money to the drunks "charged account" and indicated it on the paper work.. done deal.
sounds to me like your in the clear.. but I bet you won't be able to find out his address.. and even if you did he probably doesn't have a title.
good luck getting it lined out.. i'd say it's gonna be a little aggravating.. but probably a steal if the bike is trashed.