I just watched the footage - Trengove definitely trapped Dangerfield's right arm against him and slung him around, but the fact that Dangerfield was attempting to kick it would have made slinging him easier as he had both feet off the ground, resulting in Dangerfield being slung further around and (unfortunately) face first.
The thing is, Trengove got up and did the exact same thing to Brodie Smith a couple of seconds later, who landed on his side, and I'd say it's because Smith was trying to handball it - a sensible decision that Dangerfield didn't make.