You're right, of course, but this sounds pretty rude in English. It would be nice if there was some way to privately suggest a correction without making a big deal out of things.
As someone who speaks other languages, I know there's a point where it's hard to make progress because you are fluent enough to be understood easily and yet you make significant mistakes that nobody will bother to correct unless you ask.
As someone who speaks other languages, I know there's a point where it's hard to make progress because you are fluent enough to be understood easily and yet you make significant mistakes that nobody will bother to correct unless you ask.