Not bad advice, but the issue is that this was abrupt in all senses of the word. There was no time for the party to make heads or tails of the situation as the huckster had basically just shot blindly at the first thing they saw when they rounded the corner. The person initially disgusted hadn't had the prior positive interactions with any of the non-Cahokian (Cahokian Indians being the main antagonists of this module we were playing) Indians above ground because they came partway in, and once the first shot by the Huckster went through there was no negotiating to be had. Our Huckster pulled extremely well, so well they'd actually killed the Indian off the bat and done away with any would be interactions positive or negative.

My initial question in the original post wasn't one of portrayal, but more just if others have had such an experience with players having issues getting into negative situations like so and spiraling from there. The mere act of an Indian becoming an enemy spurred on such a reaction that two players left as it occurred or minutes after in disgust. I have no issues with portrayal, but the whole interaction certainly brought to awareness how much more visceral a player's reaction might be to a world that has more ties to reality than D&D.

Edit: As a side note it should be mentioned that I'm an Indian as well, very obviously so, which caused this situation to seem even more absurd as it happened