But in the UK, one does not ‘graduate’ from secondary school at all (which is what Hogwarts is, after all). The term is starting to spread into British English because of the American influence, where it is a correct term, but historically and correctly in Britain, one only graduates from a university (which is why those studying their Bachelors degree are undergraduates).
So whichever way you look at it, it’s bad English :)
Personally I think ‘graduated from...’ is also better in British English regardless, and would see ‘graduated’ without the ‘from’ as more an American idiom.
Good points..
when I was a teenager in New Zealand, I “finished” high school..
as you said, we didn’t “graduate” from o9r not..