It WAS in fact "German" for quite a long time (Prussian before unification)..It was a National Socialist stronghold from the early days of the party....
After beng handed over to Poland most of the remaining Germans left.. either voluntarily or otherwise...(Big surprise there eh?)
Sounds like he might have a case for citizenship if you ask me....Of course I don't know the "rules" in that part of the world.. but if he was born there before 1945.. well... He should be "German" by birth...
Utterly amazing....... Bravo!!