The ref was letting all sorts go for both sides, they just didn't twig so kept throwing themselves to the floor.
The challenge on Seriki was very agricultural, and looked a nailed-on foul, but the ref must have got shit socks for Christmas so was fed up and didn't have the patience for footballers falling over at the slightest nudge.
I am glad he gave that red. Too many defenders get away with dragging attackers to the floor on the halfway line, only getting a booking because it's so far back and their defensive partner, who averages a 30-second 100 meters, could have possibly got back to cover. It was a professional foul with no intention to play the ball, he pulled him back: off you go.