This is true. But it doesn't extend to the point that gun sales could be prohibited. Gun dealers can be subject to more regulation because they aren't protected by the Second Amendment. But if they were so regulated that the were de facto prohibited, then that would be unconstitutional: https://en.wikipedia.org/wiki/Undue_burden_standard

I don't think this has ever been tested, but I also don't think any state has ever tried to regulate gun stores so aggressively that they couldn't exist. If a state did I think it would be a virtual certainty that the Court (especially this Court) would strike it down as an undue burden on people exercising their 2nd Amendment rights.

It's also worth nothing that this article is discussing a split amongst different circuit courts regarding this issue (when different Federal Courts come to different conclusions about an issue). Thus, this issue is still up in the air and hasn't been settled by SCOTUS yet.