The differences are not really important.
Here is the diagram for the NexGuide pinout requirements:
Here is the diagram for the autoguiding port on Celestron mounts (the mounts meet the so-called ST-4 standard):
The differences in the directions of RA (left and right) and DEC (up and down) are unimportant as they are usually recognized by the software or firmware used for the guiding. These directions can also be reversed by user choice in NexGuide and programs like PHD and MetaGuide.
The mount port can deliver 5V out of its pin 1 if it is needed by a guider plugged into it. Since the NexGuide has its own power supply, there is no connection (NC) on NexGuide’s pin 1.