Galland vs Göring (according to Speer)

[CJE]

Those who read the memories of Albert Speer certainly recall the argument between Galland and Göring, when the latter was boarding his special train for a hunting party in the Rominter Heide, about the fact that an American escort fighter had been shot down east of Aachen. This argument ended up when Göring shouted: "The American fighters were not there, that's what I'll say to the Führer. Have you understood? It is an official order!".

Speer stated that this incident took place during the Summer of 1943.
But at that time, no Allied fighter was able to fly as far as Aachen and I assume Galland was talking of a P-51. However, this type did not appear before late December of the same year.

My guess: was it the P-51 shot down by Obfw Emil Schmelzinger (9./JG 11) near Attendorn (60/70 km East of Aachen), on 11 December 1943?