I think you're thinking of trademark, but this isn't a trademark claim, it's a copyright infringement claim. The legal question is whether the guitar shape can be copyrighted.
It would be odd to try this as copyrightable in the U.S, where there’s a pretty clear distinction between art added to a guitar, like PRS bird inlays, and the core body shape.
Two legal questions they will now be asked, by Thomann or LsL, are:
- if such a copyright could exist, what shape precisely are Fender arguing it would cover?
- if such a copyright could exist, would Fender (the company) have title to it?
Answering these questions could get them into some difficulty, legally. Neither are obvious and the second one is really problematic.