It's not that confusing when you look at it from a technical standpoint. Like I said, a spring piston rifle has moving mechanical parts that slam into each other when you pull the trigger. When there is no pressure build-up in the piston chamber, it will break the piston head eventually, and rip the seals, because the piston is not being slowed down by the pressure build-up. Another major reason why you shouldn't dry fire piston driven (spring or gas ram) rifles, is the build-up of heat in the piston chamber, which is not as much the case with SSP guns.
Dry firing is safe for both SSP and PCP rifles. Their principle is the same, pressurised air is being released with the pull of the trigger. That air is released by a valve that's hit by a hammer, releasing the air into the barrel where it moves the projectile forward. This doesn't involve any moving parts that might get damaged when you don't load the rifle or pistol, because the build-up of pressure has already taken place and there are no pistons involved that slam into a breech. It's as simple as that.
Look at a SSP the same way as you look at a PCP, both can be dry fired for the exact same reasons, as mentioned above. I have multiple 10-meter match grade air rifles (I'm a ranked competition shooter), PCP and SSP. Both even mention in the manual that you can dry fire them, and that this is a good training to get your trigger control practiced. I've been doing this for decades now, and we teach new competition air rifle shooters to do the same, as part of the daily training program. The modern ones have a dry fire switch, the only purpose of that is to save air, not to prevent damage.
