Nonsense.
They would have plugged a machine into the OBD2 port to clear the engine light... there is a code.
Possibly "nonsense" from you, also. If there was no check engine light showing when it was taken in there's a pretty good chance that, being car sales outfit, not a mechanics shop, they wouldn't investigate it very deeply, if at all, particularly if the ten-year old car's warranty is just about to end..