I feel this statement is not correct.
The pressure in a pneumatic system is created by restrictions. Just think, if you put 30 psi in one end of a tube, but you don't have anything on the other end, you will have an normal atmospheric pressure in it. If on the other side, you put a chork on it, you will have 30 psi inside.
For the same flow through our diffuser, we will have the same pressure just before the diffuser. If that will be increased, more co2 will pass through, increasing the bubble count.
What are you reading on your gage, is the pressure between the reductor and the needle valve, after which, you will have a pressure drop to the required pressure to push the co2 through the diffuser at the desired flow (bubble count).