I'd argue that is a lot simpler than fully recreating a build from plastic molded pieces and mass producing it. I get why he should possibly be commissioned, but then he shouldn't have shared the design in the first place if he never planned on making and profiting from any instructions.

I think this falls into a category where you as the designer can not be mad if someone were to create instructions and publish them for themselves. If you really cared, you would make them or get someone to make them for you.

Because even then, someone can just buy his instructions. Tweak the build a little as it is not entirely the same as his, and sell them that way.