Since I've already beaten HH I'm just exploring Zion park now. I came across an area called Ghost Den. For those who don't know where it is, it's slightly north of the Zion Fishing Lodge.

In a duffle bag in the area I found a note from a Vault 22 Overseer detailing their expedition to the area. He said he and the remaining Vault survivors were leaving the area due to something murdering them. He cited this "thing' as non-human.

I was wondering, is this note referring to a ghost, or something else? I found a few Yao Guai in the area, and thought it may have been them the Overseer mentioned as the murders.

I appreciate anyone who can provide insight.

The person killing them is the Survivalist, you find this out when reading his notes and stuff from the dufflebags/terminals etc

The Survivalist (Or Sgt. Vickers) killed the Vault 22 travelers for killing the family he was watching and protecting (without their knowledge) and he got a very big thirst for vengeance after they ate the women and children they kidnapped from the family.

You'll find computer terminals inside the caves with more of the story. And the final piece up on top of Red Gate.

Note that the Vault 22 people eventualy turned into those spore carriers. So that is why those things are in HH

There is a quest to get a unique Yao Guai Fist, you have to do it through the sorrows before the end of the DLC story. I'm not gonna give you details, but the Ghost Den has nothing to do with Vault 22.