This answer should not have been marked as offensive.
Mentioning Adolf Hitler is not offensive in itself (if it was, a lot of history teachers would necessarily be offensive and History SE wouldn't be allowed to exist). Nor is it offensive to say that he was "very harsh" to Jews. It's an understatement, sure, but the words "very harsh" come from the question: presumably they're not the words the answerer would have chosen to describe the Holocaust, had they been able to choose any adjective they wanted.
I don't think it's fair for someone who guessed that "very harsh" might refer to Hitler to be treated in the same way as someone who typed an answer like (warning - offensive):
Suck my dick, pussy faggot nigger bitches
The latter is what offensive flags are designed for and should be used for. From the canonical main meta post about such flags:
Even if a post is a bad post for some reason or another, it is probably not rude or abusive. The rude or abusive flag (formerly known as offensive) is meant to be used only in extreme cases, like hate speech, abuse against people, or abuse of the community or system.
As a rule of thumb, if you can’t justify something being hate speech or abuse, you shouldn’t mark the post as rude or abusive. Instead, you should downvote the post.
The answer under consideration here clearly does not qualify as "hate speech or abuse", and thus marking it as offensive was against SE policy. Furthermore, the voting on this meta post shows that PSE community consensus was also against marking it as offensive. Both the other answers here have been downvoted into the cellar, while comments against them are highly upvoted.
As has been noted by the answerer themselves, the answer was made invalid by later edits to the question, so it shouldn't be undeleted either. The correct course of action now is for a moderator to clear the offensive flags against it, thus unlocking the post and restoring the lost 100 rep to the answerer. (Doing so may also undelete the answer, but the mod can then promptly delete it again.)
I would like to request that one of our moderators do this, in the interests of fairness to the unfortunate @pydsigner :-) status-completed - thanks @Deusovi!