I gotta agree with this. In the opening it affirms states get to do as they want within their own borders. The document itself is talking about trading with other states. Lots of talk about imports and exports. I may have missed it, but I didn't see domestic product.
I can see this treaty limiting the selection of imported weapons on the shelves of states that allow them. I guess that could mean a bigger PITA if you want to buy an imported weapon instead of a domestically made one.