Is this 'Ant Killer' effective to kill carpet moth?
My suggestion is to find a good fogger and fog the van. Sprays and powders typically only work on the ones you can see.

As to the different products, it's important to note that many insect poisons share the same active ingredient, but at different concentrations. Ants are orders of magnitude smaller than moths, so it could be that this powder is more than sufficient to kill ants and eggs, but is ineffective against adult moths.

It's also possible this is just marketing as well. In other words, you market the same product, but label it for the different insects that people want to kill. If I have a moth problem, I'm not necessarily going to buy something labeled for ants.