In a test you have to prove your knowledge by transmitting symbols through language. If you don't "sugar coat" it, how do you expect that the right symbols will be interpreted by the receiver? It is part of the test to use the appropriate language to ensure the best understanding of what you are saying. Nonviolent communication tries to do exactly that and is essential to this end.
You can argue that since the professor understood what was being said, the language shouldn't matter, but it does. If again you don't use the correct language you risk offending the listener so much he can't get past that. After all you are dealing with humans, not machines, and in either case you are responsible for clear communication.
And the contrary view is that the professor has a pronounced responsibility to see past unfortunate framing and phrasing of intricate subject matter details. Both are worthwhile goals, I think.
In my university there's a professor that has an awful attitude towards students when taking exam, outright making them feel stupid (without saying anything, just from gestures and body language)... The plot twist is he does this on purpose. Many times he'll just give a passing grade, but the experience of taking an exam with him is terrible.
Don't get me wrong, I hate how university handles exposition and evaluation of subjects. It encourages exploitation of memorization and test solving techniques instead of focusing on the quality of the subject.
However, life is very rarely optimal or fair. The only effect we can productively have on the world is through how we approach it, instead of focusing energy on how our actions are interpreted. It is unfortunate, but that is the most logical outcome. Focus on yourself, not on others.
You can argue that since the professor understood what was being said, the language shouldn't matter, but it does. If again you don't use the correct language you risk offending the listener so much he can't get past that. After all you are dealing with humans, not machines, and in either case you are responsible for clear communication.