It's what you quoted. I never posted in the theory thread, but I've written essays at this point how the Oni Giants (BM calls them Ancient Giants) or Oars' Race, were tied to the PH experimentation. At first I thought Oars and that group of giants were man made, but then I saw Kaido. Then I thought Kaido, along with other people, came from PH.
THEN the Numbers were shown, all being Giants with horns last year. I kept making the same comments. Its in no way just my idea though. Its been added and morphed by a lot of people so I wouldn't ever claim it as my theory.
Like now I am totally believing Kaido is from there and BM rescued him and the Numbers before joining Rocks. Kaido is an even more failed version of the Gigantifcation experiment