Saying Pop isn't worrying or showing concern because of his stress on positives isn't quite correct in my opinion.
Pop is a good motivator and master of working on the team's psyche. Right now he realizes that the team is playing without confidence. Earlier in the year the Spurs were clicking on all cylinders. This led them to play with confidence.
The starters could run up a score and then Pop could bring on the bench players. The bench absorbed that confidence and played well, with their offensive numbers up and their defense tigerish. Their shots were falling because they were loose.
Now the bench comes into the game without much confidence. They know they HAVE to produce and they tighten up. It's a different situation and far different psychological position for all concerned.
So Pop tries to buck them up. It's not a good time for giving them with the result of putting even more pressure on them. It might be counterproductive.