I don't get how this is a gaffe.
Advising people to buy a double barrel shotgun is not, in and of itself, a gaffe.
The gaffe comes in his explanation in why it is superior to an AR. He said he told his wife if she hears anything outside their home, that she should grab the shotgun, walk out onto the balcony, and blast into the night sky.
He guarantees us that this will take care of any potential problem and so therefor noone needs a rifle with a 30 round magazine.
I would put up a link but every one I've found forces you to sit through a long advertisement.