That is a misleading description, since he started at the Realschule in Linz the same year that Hitler dropped out, and both were 16 years old at the time. Also, they were from very different social classes; Wittgenstein was a boarding student (his wealthy family lived in Vienna) while Hitler was a day student. Wittgenstein needed a lot of private tutoring, because he arrived unprepared for the standard courses, so he probably didn't even have the same classes as Hitler, who had been a student for a few years. It's unlikely that they had any kind of personal relationship.
Nevertheless, once Wittgenstein became a kind of cult figure in intellectual circles, his opponents were always looking for some Hitlerian connection.