It's one of those short stories from ARD that makes one laugh over the degree of effort put into something by the Germans.
Germany maintains a list or registry of foreigners within Germany. If you go and ask the Federal Federal Commissioner (Weise), he'll tell you that approximately 10 million people are listed with a foreign nationality (5.7 million from non-EU countries).
Evidently, they've hired a couple of folks and poured over the data listings, and have come to realize that at least ten-thousand individuals....are erroneous in nature (they left, died, or just disappeared).
In one case....they a guy is listed or entered on the list from 1921....but obviously long since dead.
So, this has some folks a bit worried because there's a lot of political actions going on and people using the registry list for budget reasons. AS Weise kinda hinted....you don't want a false list to give you some indications of things.
Who are the ten thousand? Unknown. Some might have simply got in a car and left. Some might have gone on a vacation and died back in the home-country. You just don't know.