This sort of denial happens every once in awhile because of differences in the definition of misdemeanor between several states and the federal government and the fact that the Federal prohibition applies *NOT* to misdemeanors but rather crimes punishable by more than 1 year imprisonment. Many states have, or had, misdemeanors punishable by more than 1 year in prison that trigger the federal prohibition; Maryland, New York, Georgia and Florida just to name a few I am aware of. It is BS and could and should be changed at the Federal level but they hope to gradually move all of us into a prohibited category so they will take no action.
You should note well that the exact prohibition of the law is the purchase of a weapon from a FFL. It does not prohibit ownership or possession of the weapon by a non-felon. This guy could purchase a weapon in a face to face private transaction, except in those states, like California that require a check for every transaction and is why they want to do that at the Federal level. They call it the gun show loophole but it has nothing to do with gun shows and everything to do with disarming the public.