Actually the French authorities would have little problems tracking and proving he had left France, motorway tolls, cameras, checking credit cards etc, but the point is why would they commit such resources?
Knew someone who got done for cross EU border crime a few years back (not a friend, a business customer) and it was astonishing how much the French authorities knew and how quickly they got the info together, but he was “of interest” once they’d found large amounts of illegal substances in his vehicle, if your only crime is leaving France for a few weeks I doubt you’d get a pull, unless they had an automated system linked to your registration number.