Minecraft: why does this item have two protective enchantments?

In my survival world I have had a zombie XP farm for a while and came across a strange object while farming. One of the zombies then "gave" me his gold boots. However, these have two protective enchantments (protection 3 and spring case 4).

That can't really work. Neither over the magic table nor over the anvil.

Why is that? Is that supposed to be a bug?

Is nothing special. Feather Falling is not a protective enchantment and can be enchanted at any time on an object with protection, fire protection (I don't know that in German), etc.

Just give it a try in the creative.

Ferderfall is not a protective enchantment that has the effect that if you fall down somewhere that you do not get so much damage that is quite normal that the item can be protected

Featherfall is actually not a protective enchantment, but rather an effect. Better to keep the boots, they are very useful when fighting the Ender Kite.

I killed the dragon a long time ago.

But since they only have 3 durability points and are made of gold, this is of little use.