Hands around the neck.

Griquas have the ball in a maul and are inching it forward. Bjorn Basson is in the midst of the maul, his head sticking up above the maul. Jonathan Mokuena (18) of the Golden Lions grabs Basson around the neck and twists.

The referee immediately blow his whistle and eventually speaks to Mokuena who looks mystified.

Referee right?

Law 10.4 (e) Dangerous tackling. A player must not tackle (or try to tackle) an opponent above the line of the shoulders even if the tackle starts below the line of the shoulders. A tackle around the opponent’s neck or head is dangerous play.
Sanction: Penalty kick

This applies in this case in a maul as well as in open play. In fact what happened here could be potentially more dangerous as the player is pinned in the maul and pulled  by the neck in a different direction.

It is possible to consider a yellow card in such a case.