Yes, NOX emission are a product of high combustion chamber temps, not to be confused with engine temps. Raising the compression on an engine will raise combustion temps. NOX emissions are produced when the combustion temps are above 2500 degrees. What the EGR does is let a controlled amount of exhaust gas into the combustion chamber, which is inert and doesn't burn. This inert gas takes up space in the combustion chamber so less of a air fuel mixture will enter the combustion chamber, effectively lowering the compression, combustion chamber temps & NOX emissions.  The reason I run the engine at 2000 RPMs before the smog is to make sure the Cat is at operating temp. Catalytic converters are more efficient when at operating temp. allowing them to burn off more pollutants (CO, HC, & NOX).