Clearly, his ignorance suggested he had no intent to offend, yet the female professor was offended. There are two important issues here. First, if we spend all our time watching our words and using inoffensive language or hedging everything with caveats, we will be dull and will not be able to communicate because no one will listen.
For instance, “An eye for an eye will only make the world go blind” could be replaced by “Revenge reduces collective welfare”. The latter is short, inoffensive, and pithy, but meaningless for most listeners.