The reaction of the people is quite understandable. Not having been witness to the spiritual events that had led to this overwhelming by the spirit, the people see only a roomful of people as though dead, and among them a Nephite, the very definition of an enemy. It is not surprising that this should be the Nephite’s fault (which was, in fact, actually true) and that it be counted as evil (which was not true).
Cultural: The most interesting statement in these verses is the simple fact that the people could have entered and seen Ammon, and declared him a Nephite. We must ask ourselves how the people would have known that he was a Nephite. In the days before photographs, newspapers, and television, individuals would seldom be known by face unless one had had direct personal contact with them. Ammon had either been among other servants, or in the court of the king himself. It is not likely that all of these people would have known him. It is also probable that they had heard of him, for even though they might not have seen him, certainly the news of Ammon and his feat at the waters of Sebus would have traveled rapidly through the palace.
What we cannot tell is whether or not there was a physical distinction between Nephite and Lamanite. It has been traditional in the church to suppose that the Lamanites had Native American pigmentation, while the Nephites were white (or whatever their Israelite ancestry would have made them). However, there is never any indication in the occasions when Lamanites and Nephites meet where there is any remark about skin color as a means of differentiation. Indeed, when we learned of an earlier Ammon who rescued the people of Limhi, he was taken for Lamanite when he was a Nephite by birth.
When the people recognize Ammon as Nephite, they must have done so either on his reputation, or clothing. There is nothing that would indicate that they could have recognized him by the color of his skin.