“Raiining cats and dogs” is not of American origin.
Nobody said it was of American origin. You're putting words in the parent commenter's mouth and then choosing to argue against them. That's why people take issue with your comment. If you want to contribute to the conversation without coming off as argumentative then frame your point as adding to the conversation not as an argument against something that wasn't said.
Yes, and it's used in many other places in the world that isn't America either. That doesn't change the fact that it is widely used in America. You may not have intended for your comment to come off as argumentative. But it did. You're the one that joined the conversation by explaining that it's not an American saying. It is a common saying in American English which is all the parent comment asserted.