Without knowing what subject matter he regularly teaches and the purpose of showing the video to students, one cannot say what he should be teaching.
I don’t care if the teacher taught knitting
There was a time in this country when we were in a world war. Many German-Americans, in fear of being interred or losing their jobs and homes, hid their family Bibles and rushed to change their names as an outward sign of loyalty to the USA. For years after the war, having a German surname was a handicap.
promoting bigotry -to children- towards someone of German ancestry simply for changing their name to an anglicized version, is exactly the same as promoting bigotry towards someone of Cuban ancestry for changing their name to “Ted” or someone of India ancestry for changing their name to “Jim”.
The school made the right call.