A piece of equipment could be left repaired due to damage, and I could easily imagine the repairs being hasty or haphazard, given they're in a war zone, due to lack of materials. So it's not that far fetched.
Yes it is far fetched. Most equipment left behind was sabotaged, as is the nature of war.
The phrase jury rigged means "use what you have to make it work". It's a logical corruption that you jury rigged the jerries equipment. It makes no sense at all that you would even find it worth mentioning that the Germans repaired their own equipment.
The logical origin is that the uses were using Jerry Rigged to mean Jury Rigging German equipment. Not that the Germans would also Jury Rig their equipment, that's like inventing a word to say they also tied their fucking shoe laces.
