Let’s say you are right. How is that reconciled with the swastika comparison?
Did the student have any sense of this situation before making a cross? Creating a simple cross or a sophisticated crucifix are two different things.
It's easy to assume that the teacher is a knee-jerk secular humanist and chose to criticize what was supposed to be an easy target - a religious symbol.
If the artwork is sufficiently advanced to show a real effort then the student should sue or whatever.
Hopefully, if the student sues and the artwork becomes public domain, we won't be embarrassed by the lack of effort and imagination that it took to put two pieces of clay together at right angles.