Without the grip safety depressed, the "SA safety latch is engaged". To disengage the safety latch, press in the grip device.
How did a police officer manage to ND his Glock as he reholstered it if the Glock's "60% cocked striker" is so freaking safe? Duh, he PULLED (or pushed) THE TRIGGER. Now, just maybe, if he had been handling an XD, just maybe, his hand would not have been on the grip safety at the same time and he would not have had the ND. At least with the XD he would have had one additional chance to not accidentally fire the gun.
I think we need to keep in mind that an accidental discharge is different from a negligent discharge. An ND means the person did something stupid. An AD means something truly accidental happened, such as something getting into the trigger guard and unintentionally pressing the trigger. You can have an ND with ANY firearm ever designed because nothing is ever fool proof. You find me any safer design and I'll find you a fool somewhere to defeat it.
With a Glock, you can have an AD as explained above which would NOT result in an AD with the XD if the person pays attention to the grip safety. Tell me how one could have an AD with the XD that woud not also have resulted in an AD from a Glock?
Remember, the XD is classified as "SA", but it employs a DA-style long trigger pull. It does not have the "hair trigger" of a traditional 1911-style SA.