Protection and Projectile Protection Naturally Stacking

I was enchanting my diamond helmet with a level 3 enchant, which displayed that I would get at least Protection III, and I thought that was worth it so I enchanted. When I pulled the helmet out after putting the enchantment on, it also had projectile protection IV on it, which is a bit of an anomaly since Prot and Projectile Prot should not be on the same piece of armour, unless forced so using commands. I have provided a screenshot of right after I enchanted the helmet. No commands, mods, or other altercations have been used, I'm playing vanilla 19w05a.