Skeleton trap dropped impossible boots

A skeleton trap spawned in my world, I went up to it and summoned the 4 skeleton riders and killed them, one of them dropped gold boots at 8 durability with the following enchantments: Protection III, Projectile Protection III, and Blast Protection I. I know that this is impossible to do without commands or mods (I was in vanilla minecraft), so I don't know how this happened.

To reproduce:

1. Summon the four horse skeleton riders
2. Kill the skeletons with a thrown trident (enchantments: Loyalty III, Impaling V, Unbreaking III, Channeling, Mending)
3. It may drop these boots I'm guessing

It is possibly a problem within the loot table.