There's absolutely no issue at all with that being out. The ball is still returning from the outfield when Curran leaves his ground. Staggering that Curran left his crease, even more so that Pooran called him back. Curran is there in the last over and the Giants win by just 2 wickets off the last ball!
Pooran was overruled by his coach, Flower.
Question is, would Curran have run if the ball coming in from Pollard's throw kicked and bounced over Pooran's head? Of course he would.