User blog comment:Kanehasegawa/MUST READ, MAGICAL CHEST REVEALED!/@comment-27456836-20160323082947

Uh no. Supercell did NOT make you get a Magical Chest at winning 21 games. There's a   Chest Cycle, and the thing is, you can start anywhere on the cycle. So you and your friend probably just got lucky and started exactly 20 chests before a Magical.