As someone who spun and did 2 360s on the highway many many years ago, and have taken multiple track classes and many many track days since then, here is what I think happened.
if you look, he was carrying momentum into the median. which means he accelerated during the lane change pretty aggressively.
Mistake 1 and primary mistake was he was going too fast with too aggressive at of an angle.
Mistake 2 and the kiss of death was he braked hard (see slomo at 43sec mark on the video). First rule is you cannot brake as this shifts momentum to the front which is already hydroplaning and the rear will swing around.
Once he made mistake 1, the DSC (if it was on) should have kicked in and he should have only steered minimally. braking just doomed him.
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