Looks like he let off the throttle too quick in the corner... if in a corner, especially in slippy conditions, abruptly letting off the throttle you will give over stear. You need to stay in the power band, don't abruptly let off the throttle, and if you start to get over stear, you need to stay ...
He did do Broup B... from what I know, he drove a Lancia 037, Escort Cosworth RS and I think something else. He wasn't greatly successful, but he's a great driver none the less.
Looks like he let off the throttle too quick in the corner... if in a corner, especially in slippy conditions, abruptly letting off the throttle you will give over stear. You need to stay in the power band, don't abruptly let off the throttle, and if you start to get over stear, you need to stay ...