How do you figure? The Glock trigger pushes the striker back, and when it reaches its release point the striker is released and the gun fires. In a double action semi auto pistol the trigger pushes the hammer back until it gets to its release point, when it does the hammer drops and the gun fires. Seems similar to me.
The Glock Safe Action is neither DA or SA, but is much closer to SA.
If you were to pull the trigger on a Glock that is ready to fire, and the round doesn't fire, can you simply pull the trigger again and have it pull the striker back to release it again like a DA auto would do? No, because at that point, the striker has already dropped, and no amount of trigger pulling will cock it again unless you rack the slide. It operates just like an SA auto that needs to have the hammer cocked before pulling the trigger to allow the hammer to fall. The Glock needs the striker cocked, by racking the slide, to allow the trigger to drop the striker. Additionally, when you field strip a Glock you have to pull the trigger to decock the pistol. If it actually were a DA pistol, and the trigger did all the cocking, you wouldn't have to do that.
Think of a Glock Safe Action as relative to a CZ 75B.
Glock marketing, and many users, would have you believe the partially cocked, ready to fire Glock is in the same status as the CZ75B in double action mode with the hammer at half cock. With the CZ 75B hammer at half cock, the hammer is partially cocked and you complete the cocking by pulling the trigger. If all safety devices were to fail (no matter how unlikely that would be) the hammer of the CZ 75B at the half cock position simply doesn't have enough stored energy ignite a round.
The cocked Glock striker is closer to the CZ 75B in single action mode. When in single action mode, the CZ 75B hammer is back, but when the trigger is pulled, the hammer cams back further and then releases. That's what the Glock striker does. When you load a Glock, the slide cocks the striker back, but not all the way. Pulling the trigger cams the striker further back and then releases. The cocked Glock striker has enough energy to ignite a round.