Since SAT (customs) is a federal department, I wouldn't think a governor would would have the authority to rescind customs regulations.
Cozumel's airport INM (immigration) and SAT are sub-stations of Cancún's. This being México, there's no reason they might not have entirely different policies.
I never encountered any issues, and I've brought a lot of weird stuff over the years. Then recently I was bringing my son't brand-new expensive laptop and got dinged for duty. Then when I was bringing a "solar generator" (big-assed lithium battery and solar panel) I had to pay duty. When my wife later brought a second one, they just asked her questions about it and did not assess any duty. It was very likely the same officers.
I will note that the other computer I had when bringing my son's was my 5 year-old MacBook Pro, the original price of which (loaded) was about the same as the new one. The current value of my computer was less than 20% that of the new one. You only et one guess on which one I had to pay duty.
It's not a fine. It's import duty.