For those who don't know the rule, and quite a few here don't... NFHS 2023-24, 7-1-5w: it is illegal to do, "a back flip from the standing position, or a front flip and/or front hurdle over an opponent in the standing position." Clearly wasn't a back flip. Not a front flip, he never went forward like a summersault, he spun around like frisbee, always facing downward. He didn't hurdle him, he spun around the side.
Not a back flip, front flip or hurdle. So, doesn't matter if opponent was on feet. You can clearly see in the photo you posted, he is spinning around, not hurdling and he is face down, not flipping. You didn't understand the rule of didn't see what happened.
The only real question is was there reaction time. That's a subjective call by the ref(s), which is often debateable.