It's funny because in Germany we have a similar phrase "swallowing the toad". I think the idea is to swallow them whole. I think French cuisine generally only serves frog legs, not whole frogs?
And yeah, just the legs.
Also they once were a very "poor" (please read as cheap) meal, while nowadays they tend to be "gourmet".
BTW. I had also expected the article to be about actual frogs: about how endangered some species are, or how the flesh may contain pollutants or diseases.