You've little idea to know whether or not the car was stolen and simply not reported as so. Dude could have had the owner in the truck. You said it was a taxi but not a town car, so as long as you've got the plate number, the car attached to it will turn up at some point.
Regardless, since he gave you false information I'm sure the police and/or your (and their) insurance company will be interested to know about all this. Something fishy is aloof, so just do what Dunkel said and good luck.