This does come off as rude! There are ways to give constructive critique and this isn't one of them. It can make artists that aren't confident, feel even less worthy about their abilities, while making the person that told them that look VERY boastful.

There are great ways to help others improve, and give proper critique, however! I advise anyone who is looking to get better to always listen to suggestions, read tutorials, and ask artists that they admire for input!