Oh honey, don't sweat it

Chibi is derived from the japanese word for short person

are you sure? My Japanese teacher said it was fat person but watevs

It's one of those words that can take on different meanings depending on the context. It's derived from the word for short person, and there are different ways in which it can be used. Your Japanese teacher probably uses it in that fashion or has been in an area that uses it for that, it's not uncommon for things like that to happen in any language.