I interpret it as an adjective; there are already a variety of alternative burgers such as chicken or turkey burgers. They're typically meat, but I guess I've never assumed they had to be; just that most plant-based sandwiches are closer to other things. Interestingly, salmon in patty form is usually referred to as a salmon patty even after being cooked (at least around me).

I don't find it at all confusing. A veggie burger is a patty made of veggies, just like a turkey burger is a patty made of turkey. The only case where I think it might be confusing is if the patty is made out of something that could plausibly also be blended into the meat of a regular burger. If the box said "jalapeno burger" and inside was veggie burgers with jalapenos in them, I'd feel mislead.

>Just require people to be explicit about what the burger/sausage/cheese-like thing is made of and that's all, surely?

The problem is while some products use packaging that clearly indicates it is non-meat based, there is plenty of packaging that does not. I nearly bought some plant-based food recently because it was looked similar to meat-based versions of the same thing, and I only happened to notice it was "chicken-style" (the "style" being in very small lettering and so offset from the word chicken that it was practically detached) when I took a second look to check the cooking instructions. It wouldn't have hurt me to eat it, but I would have been disappointed to only find out when I went to start cooking. I live with a vegetarian, and have tried a number of meat alternatives and not been impressed by any of them so far - while some are ok as their own product, nothing I have tried was a good substitute for meat.

I understand that some companies want to market their products as "indistinguishable from meat", such as appealing to people who became vegetarians for ethical reasons but still crave the taste of meat, but I am a firm believer that packaging for food and other important items should follow the principle of least astonishment, and that using terms that have historically referred to meat products to market non-meat products in a way that can mislead or confuse consumers is unethical and should be regulated.