The Glock can not be fired only by pulling the trigger. That's what DA is.
The Glock can only be fired after it is cocked, by pulling the slide back.
That is not what DA is.
With the BATF definition, Double Action only refers to what the trigger mechanism does.
The Double in the DA is that it both retracts and releases the striker/hammer. If it only performs a single action, releasing the striker hammer it is SA.
Even though the Glock striker is partially cocked by retracting the slide, the trigger mechanism still pulls the striker back and releases it. 2 actions, Double Action.
What is your definition of Double Action?