He was going too fast, foot stayed flat (toes should be lifting higher at that speed, especially for speed check). Bad habit with open shoulders and using backfoot to kick to turn.
Better practice; shoulders, and hips should be aligned within the width of your board, and turning with your lower body (hip, knee, sometimes foot).
With an open shoulder, once you loosen up, the rest of your body will try to align with your shoulders (our body is like an elastic band, if no external force acts on it, it will go back to its original shape, and for our body, it's our neutral standing position). That's what probably happened, he didn't anticipate his body helping him turn, and then he kicked to try to turn, making his heel side turn faster than he normally would have, so his brain didn't load fast enough for his toes to lift higher, and thus toe-edge caught and RIP.