Because Mizzou was out-rebounded.
Against one of the top rebounding teams in the nation.
I need 75 words, so how about a comment about K-State getting screwed? They may well have lost the game, and there certainly is no guarantee they'd even have tied it, but an excessive celebration penalty for a quick salute to the crowd? It's certainly possible that the exact letter of the rule specifically points out a salute, but his behavior was clearly not to taunt his opponent.
Silly enforcement of that rule.