In that case, a question along the lines of I'm curious why... would have been perfectly appropriate. I don't see why just comes across as I know better. But perhaps English isn't their native language.
Or perhaps there are regional variants of English where this is a normal way to ask a question. There are probably lots of idioms that work in one area but would be offensive in another, and it's not always easy to predict.
For what it's worth, that kind of surety that one knows every region comes off as rude in quite a few places as well.
For example, it was quite amusing and annoying watching a coworker insist that the rural area I originally came from isn't rural because it doesn't meet his personal definition, though he had never even been to the state.
"I don't see why" is a valid way of expressing a lack of understanding combined with a spirit of collaboration where I am from.
