Steal or just borrow?

I was handing out fliers at the subway station. I parked my tricycle next to an unlocked bicycle. Two guys came up to me and asked me if one of those bikes was mine. I told them that tho one on the left was mine.
They confirmed that the one on the right wasn't mine and then proceeded to take the bike on the right. I told them that if they steal the bike I'll call the police. 
They said that they weren't stealing the bike but only borrowing it. Since there are a lot of guys out "borrowing" bicycles, keep yours locked.

~Tim~