And Polish Americans and Irish Americans share October and Irish American history month is in March. But only black american history month is taught in schools- at least the ones around here. Not Native American, Irish, Italian, Polish or any other that I'm aware of.
So if a student complains that they only get one month, as in the example that started all of this, then to respond that they are lucky to have one celebrated is not inappropriate, IMO. Are you saying that the student was correct and they deserve more? If so, why and to what purpose?