Looks like the blades flexed during low G.
No low g there, he was at 1 g in a hover, but when bowing to the crowd, he was making the nose go down while pulling the disc back - first time was OK, but with the extra momentum of the second nose down, the tail just got in the way. Silly boy.
Probably comes under the "Streaker's defence" - it seemed like a good idea at the time.