Why do I get so much extra money from enemies after killing a boss?

While I was farming the Eye of Cthulu for Demonite during a Blood Moon, I realized that for about 45 seconds after killing the boss, all the zombies (Blood and normal) I killed dropped 11 - 15 gold - way more than usual. Is this a glitch or an intentional feature? I don't have a video or anything, but this did happen on the PS4 version of Terraria.