Trey Parker and Matt Stone, in hindsight, thought the story would have been better off split up into three episodes and not two, mainly because there was a lot of content left that they wanted to use but not enough time.
Felix Kjellberg (PewDiePie) was recording the last part of the episode in Tokyo, Japan, while he was there on vacation.
When hologram Kurt Cobain is singing, a bunch of Twitter messages come up. One was from @D_Grohl77(Dave Grohl) saying "I miss you Kurt so much.... #courtneydidit." Then a second one by @CeeLoveHole(Courtney Love of Hole/Kurt's widow) saying Smashing Pumpkins were better. This, of course, stems from the hatred of the two after Kurt's death and Courtney's old flame of Billy Corgan of Smashing Pumpkins. Great joke from Matt and Trey.