I would guess the locking toggle was mangled by someone unfamiliar with Lugers, who didn't know to pull the top back or press the barrel down on a table top. So, they resorted to using tools - screwdrivers or pliers to try to twist the bolt around.
Do you have a photo of the barrel underside ?
I'm having trouble making out the full serial number (5169 ?) and if it has a suffix
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