So as I understand it

Naka was 2 pts behind Ian for first, was playing Ian, and had 2 more games after that.

If you beat Ian in this game you're behind by only 1 pt with 2 whole games to make that up for first to win the tourney and play Magnus for the championship.

Naka decides to purposely not risk anything and go for a sure draw, because if he tried to win he'd probably lose ... But the whole point of this tourney is to win 1st so you can play the champ.

The slight chance that Magnus decides not to play is not something that should dictate the decision here imo, you play to win.

In the end Naka finished 4th... But when he decided to purposefully tie against Ian, that's when he self decided to not try to win the tourney anymore.

Maybe the 3.5 K in prize money per half point influenced that decision?