Why is that the comparison being made?

Because beyond meat is junk food, whether it’s sold in supermarkets or restaurants.

I believe the claim being made here is that "a beyond burger" is a thing which fast food chains and supermarkets will offer as an alternative to "a beef burger", that almost nobody will make their own burgers.

I have no opinion about the economics of the brand itself; as a vegetarian I've always thought they were over-priced, and also that it was a shame I don't have a huge range of alternatives, as I actually like spicy bean burgers and can't find them any more*. In fact, because of the limited alternatives in my local markets, I got a kit for making my own burgers from dehydrated soy mince and/or mashed kidney beans.

* I don't know how much of this is "bean burgers are no longer popular" vs. "I moved country and Berlin has never heard of them"; for Quorn I do at least know it's the latter.

People who make their own burgers will always make healthy burgers, whether meat or vegan.

People who buy burgers or eat out are likely to get less healthy burgers, if you look at highest selling supermarket burgers, both meat and vegan options are ALL high in salt for example.