I know that some misdemeanors bar gun ownership based on stuff like the Lautenberg Amendment (domestic cases) and in other state matters where the possible jail time is 2 years or more (can't recall if that's in the '68 GCA or something more recent).
The weird part here is that a conviction from 42 years ago actually got uploaded into NICS. Hell, that's 1971. I suppose it *could* have happened as part of a court clerk's modernization project - scanning old files and building a digital database. More likely, IMO, is the possibility that federal money is being spread around to pay for sifting through archived files for this stuff.
It is beyond odd.