It seems more nuanced. What does it mean that the command doesn't exist? Every serious Emacs user has their own personal bindings, some of those for their own custom commands. But "M-butterfly" suggests more rare hackery, though seemingly trivial for the hypothetical butterfly hacker: they have a "butterfly" key in their keyboard layout.
> You can type ‘M-x butterfly C-M-c’ to run it. This is a permuted
variation of ‘C-x M-c M-butterfly’ from url ‘https://xkcd.com/378/’.
From the documentation. I don't know why they didn't make it the same, but this is how it is, though maybe because M-butterfly is rather hard to press.