To add on to what you said, only the lower recievers for most guns have to be registered. Someone could hypothetically get every other upper part for a pistol or rifle delivered directly to their door or PO box with no questions asked, and then just hypothetically 3d print the lower reciever.
It’s not that the union head should be neutral. The head of a union should be openly and unapologetically pro-union. Going on a podcast and agreeing with someone who is right-wing extremely anti-union, is a very bad and traitorous look for the head of the union.