Too early to assign cause, but clearly not a stall. Under control, no wing rock or flutter, this means the pilot misjudged a) the top of his loop altitude (too low), b) sink rate, c)altitude to recover, or any combination thereof.
High speed stall. . .not sure what that means. Are you referring to an abrupt yank on the stick that results in disrupted airflow (stall)? It clearly was flying under control, no abrupt flight control input. . .it was a classic controlled light into ground.
Sad.
Maybe he was too low at the top of the loop. There is no wing rock or flutter in a high-speed stall, just loss of lift and a high sink rate. He was nose-high when he hit the ground.