Josh Dun has been a fan of Blink-182 for a long time and is good friends with Mark Hoppus. When Blink had to cancel their South American tour dates twenty one pilots were asked to fill their slot and performed a Blink cover at each show.

Clips from:
Josh playing at Blink show:    • The Party Song, Mutt (ft. Josh Dun - ...  
Twenty One Pilots interview;    • twenty one pilots: Interview with ALT...  
Mark Hoppus radio interview:    • Debby Ryan & Josh Dun interview on Ma...  
Josh South American interview: https://www.youtube.com/live/FJ7IPAAF...
Argentina: https://twitter.com/Pogopedia/status/...
Brazil:    • Twenty One Pilots  - Lollapalooza Bra...  
Chille: https://www.youtube.com/live/-aPrmknE...
Mexico: https://twitter.com/keonstrash/status...
Paraguay: https://twitter.com/blink182py/status...