What they are saying is don't screw the CO2 bulb into the unit until its hooked up to a keg.
Otherwise you shoot about 900psi into the plastic top of the charger and the unit fails (i.e. it becomes several smaller non-functional pieces).
To get more to your question though, yes, they're assuming you don't have much pressure inside the keg, such that attaching the valve and empty charger unit first. The valve in the charger is going to prevent your CO2 headspace from emptying out. I'm assuming its only 12psi (serving pressure) inside the keg, so popping on the gas disconnect won't be hard.
Primary: English Mild
On tap: Pale Ale, Lancelot's Wheat, English Brown Ale, Steam Beer, HoovNuts IPA
Bottled: MOAM, Braggot, Raspberry Melomel, Merlot, Apfelwein, Pyment, Sweet mead, Cabernet
Gal in 2009: 27, Gal in 2010: 34, Gal in 2011: 13, Gal in 2012: 10