Don't know what the tuner actually meant, but the fuel pressure, controller by the main fuel pressure regulator, is not supposed to rise. Most efi-cars have a rising rate fuel pressure regulator giving a fuel system pressure of 2 bar + manifold absoute pressure. If he wasn't familiar with RSTs, then he might have noticed this.

If on the other hand, he knows the RSTs inside out, he might have meant the electric control pressure actuator. This is what b13nde was on about. The fuel control pressure only takes care of all fuelling corrections like acceleration and WOT enrichments and overrun fuel cut off.