That spring (in the picture) is the slide catch spring, it holds the slide catch down. The mag safety is back on the sear block end. Hang on a few minutes, I've got the video (AGI) I'll run through it and see what I can find.
OK, looked through the video, there is no return spring on the bottom portion of the trigger, there is a square-ish surface that bears on the bottom of the trigger bar, that's all. The guy on the video did mention that the pins in the trigger are quite tight, it might help to put a drop of lube in the pin location and wiggle the bottom of the trigger back and forward to ensure it's free to move forward. Also, because it relies on the trigger bar to reset, the trigger bar must reset (cocked pistol) in order for the trigger safety to function. The trigger safety itself (the bit that blocks the trigger movement) is a little plastic wedge that contacts the frame unless it's pivotted out of the way by your finger.
