A had experience, A told B, B told me. If the story is a lie, A is the one who lied. But I will never know, because I do not talk with B anymore (lives in another country) and I have never met A.
Another possibility is that it happened, just not the way I was told. Perhaps only one person stood and did the salute, perhaps the salute did not happen but the teacher instead though Adolf Hitler was head or state (or someone from his faction). Or I just remember it wrong, it was not A who had the experience and it is just an urban legend. It was 10+ years ago, after all.