Great little story! Such vivid details, I could smell that muggy swamp.
Absolutely racism first and foremost, but not only that, a differentism was in play.
Anything about someone that sets them apart as different, anything not towing-the-line of a person's idea of "normal" is suspect and fair game for scorn, ridicule and mistreatment.
It happens every day. We expect people to conform and fit the mold and when they don't -- looks, actions, thoughts -- there are some that find that threatening, a personal affront, and they must act.
The big cats got the Baxters: I give this passage to you as proof.
"They said that a cry which had been heard just before dusk and just after, skittering across the darkened waters, was his calling cry to the big cats, and at his bidding they came trooping in, and that in their company he swam in the lake on moonlight nights, sporting with them, diving with them, even feeding with them on what manner of unclean things they fed. The cry had been heard many times, that much was certain, and it was certain also that the big fish were noticeably thick at the mouth of Fishhead’s slough."
Before Fishhead fell into the swamp, he sent out his cry, and he brought those cats in for feeding.
"They call them man-eaters and compare them, in certain of their habits, to sharks."
The only real group that accepted Fishead for his true nature heard that cry and they came on instinct and did what Cats have always done, they fed.