Cool Fanny Pack interaction? FINAL BOSS SPOILERS

[Bistro]

So I noticed while doing a Tainted Azazel run that the 4 Horsemen spawned in the first phase of the Beast fight were dropping random pickups while being hit. I was confused about this until I died and got the death screen, which showed in the "killed by" box a picture of Isaac's face.

Apparently the game literally treats these enemies as an extension of the playable character (presumably for story reasons), hence why the Fanny Pack that I had obtained earlier was working on them. Or maybe it's a bug, but it's a cool interaction if intended.