I looked it up on the Janome website and it says auto-declutch is: Automatic de-clutch bobbin winder – which means the machine automatically stops the needle from going up and down when you are winding thread onto the bobbin.
I found this description for push-pull on another site: When you put the bobbin on the post to wind it, you must push the bobbin to the right then press the foot control pedal for the thread to wind on the bobbin. Once it is done, push the bobbin to the left. I'm not sure, but I assume you don't have to push the bobbin to the right in auto-declutch.