I get it, I do that all the time while writing and building games!
Glad you like the Xenos, tbh I didn't heard about Manhunt until Idle Cartulary mentioned the module In her review of Xeno. And I still haven't had the chance to take a look at it haha.
The inspiration for the mechanics come from The Witch is Dead by Gshowitt and Cy_Borg/Mork Borg.
And for the Xenos themselves:
BONE is inspired by the alien in "The Autopsy"
KNIFE by the hydralisk from Starcraft
MEAT by the Tank of Left 4 Dead and creatures from similar games
GRAVITY by the Cthulhu mythos and Warhammer 40k