Players react to loose pucks based on hot/cold and awareness.
It's not momentum, it's the advantages in the game that create these kind of effects.
There are few players with high awareness, but the advantages bump the hot/cold to make players do things like intercept pucks and toddle on checks.
Example... In GDL, Sweeney doesn't react to loose pucks and intercept passes, however he does in Classic (Boston has a high advantage, and there are no advantages in GDL).