It’s certainly distasteful. However, I don’t think the man should lose his job or that his academic career should be sabotaged as a result of one act of bad judgement, unless there’s a history of racism and anti-semitism here. And I certainly don’t see that.
Remember, professors have extensive protections for academic freedom and speech. This was clearly a rather poorly-thought out attempt at historical relevancy–note the following quote from a Middlebury student.
“I am Jewish. Both my uncles are rabbis. I did not mind the question because, frankly, the Holocaust happened, and the gas was used. I took it at face value as an attempt at historical relevance — if he had never said what HCN was, I would not need to write this today and we would all have simply calculated some meaningless jumble of letters. Should he instead have had us calculate rat poison? The lethality of bathroom ammonium? Yes. Should he lose his teaching position? No.”