Not sure which part of that battle you thought was cheating, but Togekiss gets the ability Serene Grace, which doubles the flinch rate on Air Slash from 30% to 60%. From there it's just a question of luck. 36% Chance to flinch twice in a row, 21.6% to flinch thrice, and 12.96% Chance to flinch four times. All in all, it's about as likely as getting a freeze with the move Ice Beam.