The guy wrong on all accounts, but the foreigners are singled out here in Chiang Mai also when tourist season is busy. They always set them up in same few places.
The problem is no police enforcement of rules at point of hire.
No body should be able to rent a motorcycle if they haven't the correct license needed. A photocopy of the License should be on reverse side of the rental agreement which states conditions of helmet requirement in various languages on one page.
After that if a stupid tourist want brain injury and fine, problem belong them.
I ride a motorbike here and have been pulled up in town with helmet on few times at tea money stops.
Been asked to show my license, I Showed my Australia license to see what happens, big smile we want 1000bht, I say sorry I show you wrong one and pull out one Thai license that kills a smile.๐