My guess is he implemented this after reading Dr. Evan Osar's book. Prior to it coming out I had never seen the cue used at all. Evans thought revolves around the fact that dysfunction can arise from placing the scapula in a fully retracted and depressed position, which is what squeezing them tight is cueing you to do.
To achieve the "wrap" you should feel like you are getting activation in your upper back, but not by squeezing the shoulder blades together.
The problem is that pling is a distance game, so while it may not be optimal for functional performance and rehab, squeezing will reduce your Pressing ROM, which will allow you to press a heavier weight.