The fact that a statement has been used in propaganda has no bearing on whether or not it is correct. As the saying goes, "Ideas are not responsible for the people who hold them."

The statement was wrong because it is wrong, and I gave a citation written by professional historians demonstrating that fact.

That the statement is popular because of NRA propaganda is a separate issue. See https://www.politico.com/magazine/story/2014/05/nra-guns-sec... for a reasonable explanation of the history behind why that claim is true. And for documentation of the fact that, until said propaganda, that claim was widely and rightly rejected.

I have no reason to doubt that he has made up his own mind based on information available to him. However I also have no doubt that if he lived in any era before the NRA propaganda took hold, he would not have come to that opinion. Because it is an opinion that basically nobody ever held.