https://en.m.wikipedia.org/wiki/The_Return_of_Chef

"After leaving South Park to join the "Super Adventure Club", Chef returns and the boys quickly notice that he is acting strangely as he expresses a desire to have sex with them. They go to the Super Adventure Club headquarters and discover that the group is made up of explorers who travel worldwide, molesting children. When the explorers' leader, William P. Connelly, unsuccessfully tries to hypnotize the boys, they realize that the club has brainwashed Chef."

Pizzagate related because Matt and Trey are high profile celebrities who had a fallout with Isaac Hayes over Scientology jokes. Isaac quit the show, so the South Park guys called him a brainwashed child molester part of a secret society.