http://youtu.be/IyUJycYmwcI
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i'm no expert and its hard to see but to me it looks like by the time you got to his toes to pull down he had his other leg under it to block the calf slice.
Your knee wasn't on the ground when you locked your grapevine from top. So when you rolled you were knee to knee, instead of his knee over your shin. Not much pressure knee to knee. This also allowed him to escape his hips to the ground for the twister. To pull it off his hips have to be on top of yours.