Actually, if that is true, then the German officer was a bit lucky.
As a kid we did a school exchange to Freiburg, one English girl was taken by her temporary family to visit some relatives - the relatives did not realize that she was English, they thought that she spoke a local(ish) dialect.
You get some pretty heavy regional variations in France, Germany, Spain and the UK - not to mention Italy (I heard that the Italians used Bergamot radio operators, as the USA used Cherokee).
The actual story in the OP may be slightly apocryphal, but the Gestapo did have an interrogation technique which involved being rather friendly with the prisoner, chatting about the weather, current events, hobbies, etc, and then offering them a cigarette. After lighting their cigarette, the conversation would continue for a minute or two, then the Gestapo officer would suddenly slap the prisoner across the face, hard.
A real Frenchman/Pole/Norseman/German would let out an expletive (or expression of surprise) in their native tongue. An English speaker would say “What the hell?” (or something a lot stronger), giving themselves away.
Another technique would involve waking the prisoner up in the early hours of the morning, with the Gestapo agent saying something like “Quickly, you’ve got to wake up, we’re being rescued by the Commandos” as they shook them awake… sleep fogged brains don’t always process things rationally, causing the prisoner to reply in their native tongue.
This is a bit misleading. We have big round pies over here - sweet or savoury - as do the Irish. I’d hazard that the American pie is derived from either country. Also, when in France recently I saw lots of tartes that were round and cut into wedge-shaped slices too.
I’ve heard that the French Resistance would do something similar to determine if a downed pilot was actually a German spy or not. Bust into his hiding place in someone’s cellar at 3AM screaming in German and pointing guns at him.