How is atomic less confusing? Immutable means that something doesn't change, atomic means that it's the size of an atom or has nuclear energy
EDIT: I've learned that some people are overly pedantic about the meaning and practical use of the word "immutable", so much so that they decided to create a bigger confusion by giving another word a completely different and exclusive meaning
And it's probably India which has the most English speakers in the world (counting it as native, second or third language)