A Luger isn't a single action in the same sense that the Colt was a single action. The 1911 Colt could be loaded by working the slide, placing a round in the chamber and cocking the hammer,the hammer could then be manually de-cocked. To fire, the external hammer would then need to be re-cocked by hand.
The Luger did not have an external hammer. Working the toggle loaded a round and cocked the firing pin. While the safety could be engaged, with this disengaged, the Luger was ready to fire, and the hammer couldn't be de-cocked and then re-cocked as in the 1911 Colt and Walther P38.