Very few feral horses would actually maul you. The ones to be carefull with are studs during the summer breading season and mares with new foals. I have picked up a new born foal and had the mare charge into about 10 yards befor she turned aside. I had my .444 in hand. I have a friend who had a stud pound on the rear of the gelding he was riding. I also have videoed a stud coming at me and finally turning back at about 40 yards when my very crude expletive was yelled at him.
The one you encountered sounds like it was either a debilitated (blind, old age, deaf, truck struck,????) or surprised (up wind?) feral horse
or an escaped semi tame horse. At any rate, you did the right thing by hauling your but out of it's way!