I was curious about the whole "Weapon" thing, so I looked at the RAW:
What is happening here is that "Weapon" it is written in Katakana, so it is an "Engrish" word instead of whatever the Japanese word for weapons in general is. So it
would make sense that they don't know what "Uepon" is since it is an English word, but it is awkward when translated.
So case closed, right?
Nope
Turns out that the "Sword Master" is written in plain English and they can read that just fine. So they know English words but
conveniently don't know what Weapon is.
What a forced shitshow.