@Barry158 It is good to host with genuine idealism, I do also, but you ARE dealing with people and that has never been an equitable endeavor.
Keep in mind the generation where those that run Airbnb (and most such overnight-success big companies of the last 25 years) came from the same generation - pandering is their religion, holding people personally responsible even for obvious abusive behavior is not. If this guest was 'all angry', over something that hasn't come up before in 2 years, that was your first clue something was indeed different, unless it was your mistake of course.
I would take the vein in your public review saying - "How odd that after X amount of guests, you felt that "Y" which has never come up before". Always intellectually isolate nuts, hustlers and the mean-spirited in a cunning & smooth manner, it helps potentially future guests dismiss them that much easier. If you are going to refund money, make sure to get something in return.
P.S. #1 Like @Helen3, I have not detected a difference in Airbnb clientele in comparison to 6 years ago, except the word 'discount' now comes up a bit more often.
P.S.#2 This case reminds me of Dire Strait's song - 'Money for Nothing', which would have been a juicier title for this thread.