When I first saw it I thought it was a penalty as I though Best had put the ball on the ground. On second view I saw the ball was always in the air and thought it was all OK. Now on third viewing (with this thread thoughts) I would agree this is a double movement. He has been tackled, tackler is still in contact with the player when the tackled player is no the floor, therefore the tackled player must release.
I can understand the arguments of was he tackled, i.e. did the 9 bring him to ground or did he bring himself to ground, but on balance I'm happy to call this a tackle and therefore a penalty offence.
But given the judgement involved and it not being clear cut, I don't think you can challenge the on field call or say it was wrong. Matter of judgement, mine differs to the referee, but only on third viewing in slow-mo. On field, full speed? Happy with the call.