Probably when you installed the second linux you overwrote the boot loader instead of adding a new UEFI entry point.
But I've never had a Mac, so take this with a pinch of salt, and honestly considering things can change based on what, in which order, and how you installed things.. it could be something else.
Not as scary as a look as the one from the angry burrowing owl you met before.. but up there! Haha