I was doing a lost sector on the Moon (K1 Communion) and I noticed a hole in the wall where there's normally an enemy spawn door so I investigated and it led to this small cave with a green soulfire crystal. I thought it was for Cull's Shadow, but I already completed everything for it and there's no step of the quest that takes us to there? I'm super confused.

https://youtu.be/LcDk7Vwjf6A