> The full menagerie of shapes is too diverse to get a handle on, so mathematicians tend to focus on convex polyhedra
The phrase "tend to focus on" suggests it's not an exclusive thing. However, you're right -- it appears that the Rupert property only applies to convex polyhedra, so the article title and text is at the very least incomplete given that a sphere is a shape.
> If you start something new from this code and it becomes successful, guess who is going to come out of the woodwork and want a portion of it?
This is literally the reason lawyers exist. It’s not hard to draft up an agreement where the former co-founder transfers all rights and ownership and relinquishes any claim to the technology.