Like any category, and especially this one that is often subjective or hypothetical, you need to add a note (I usually use this one) or trivia, preferably with at most as possible some kind of reference (comparison to the source material, marvel appendix's page, interviews or articles...), in order to justify it.
I understand it may seem obvious why the category should be added, but the goal isn't to add categories to pages, but to add content, the category being a way to find the collection of pages containing said content.
Thanks to complete the involved page and you could have edited in the same way.
I added the category given that the entirety of Carnage Vol. 2 (and the island the Chthonic Temple is found on) was a pastiche of the Cthulhu Mythos - the temples are dedicated to the Great Old Ones and built using disturbing alien geometry that causes sanity damage to those who see it, after all - thinking that would be enough of a reason.
Thinking about it, I'm not sure that the Temple of Chthon and Chthonic Temple are direct homages to anything H. P. Lovecraft wrote -- I don't recall Lovecraft writing about any big temples to Cthulhu and the other Old Ones decorated with alien geometry, aside from the city of R'lyeh and the island from Dagon. Perhaps there's some things in the Call of Cthulhu tabletop game that are closer parallels, but I'm not sure.