People have been calling it a "veggie burger" for decades now.
Saying it can't be a burger is ridiculous -- it's a kind of burger.
But, I fully support packaging requiring word(s) beforehand in an equal-sized font -- "burger" reserved for beef, while "black bean burger" and "veggie burger" and "quinoa burger" are all fine.
What's bizarre is that beef burger makers see this as a threat worth addressing... like, nobody's accidentally buying veggie burgers.