The Sheriff didn't know? wow.
I wouldn't necessarily expect him or her to know, unless he or she had been involved in a case in which someone had been charged. I suspect that the average local LE officer in America has far more experience with cases involving illegal possession
of a firearm rather than illegal sale or purchase
of a firearm.
This is a good time to rehash one of the oft-repeated saws of the TFL L&CR subforum: Do not expect local law enforcement to be experts on state laws regarding the purchase or sale of firearms.