I don't like Glocks but this had nothing to do with the design of that specific design. The quote is also from an "inventor" who seems to be pushing his product.
I have seen IDPA members reverse the order of clearing a semi-suto which shocked the heck out of me. That's one of the reasons I don't believe in pulling the trigger as the last "test" whether it loaded or not.
According to one of the range tests I've taken:
Main Entry: 1safe·ty
Inflected Form(s): plural safeties
Etymology: Middle English saufte, from Middle French sauveté, from Old French,
from sauve, feminine of sauf safe
Date: 14th century
1 : A mechanical device which can fail.
Right.... If you have to pull the trigger to be sure, then you are not sure.
I seem to recall that disassembling many semi-automatic rifles, such as the M1A, require that the hammer be cocked and the safety set in a particular way ( can't remember whether "on" or "off").
The instructions with the Glock call for pulling the trigger, with the pistol pointing in a safe direction, as part of the disassembly procedure, immediately after checking to ensure that there is no round in the chamber. It may be that the striker mechanism must be de-cocked for proper disassembly and assembly.
My Kimber Ultra-Carry specifies that the trigger be pulled, to drop the hammer on an empty chamber, after checking to see that the chamber is empty. There is no warning to point it in a safe direction, though we all know to do that. Disassembly calls for racking the slide, which will re-cock the hammer.
The general rule seems to be that there is no "general rule" and that the user must know the particulars of the firearm they are handling.