I've reproduced this multiple times. If using an Elder Goddess and killing another goddess then bite/eating the corpse, a loot bag appears(as can happen normally).

However upon opening the loot bag. It has 1 of almost every learned recipe(grey quality) And 1 lesser antidote, sparkpowder, bug repellant, narcotic, and stimulant.

Very strange bug but yeah... I can reproduce it every time I kill 1 goddess with an elder goddess.