He lied on his citizenship application and on his residency application. That is the root and branch of the problem.
If he had not lied, he may have been admitted even so, and we would not be having this discussion now.
He did lie. You don’t get to lie on your citizenship application.
He was in a german prison camp - there is no doubt about that and he only lied to stop being sent back to the communists where he was surely to be killed.
http://www.geocities.com/kitezhgrad/history/keelhaul.html