Why did this happen to me?

if it was a stallion it is a very HIGH possibility that thats why he freaked out. stallions dont know any different they react as if you were a mare. your mom cant have him put down if it is not your horse. he also could have freaked out because he didnt know you and tried to test you because you were a new person. mares are just as moody i have 4 mares and they all cycle just like humans and tend to be nasty when they are cycling.