They key here is "Mauser" the rifle obviously was not a Mauser of any type ever made. A Mosin is so obviously not a Mauser to anyone that knows diddly about military rifles.
Now the deal about the Germans is that they in fact used everything they captured, from pistols to Anti Aircraft guns, including tanks, trucks and aircraft. By war's end they had folks running around with stuff from everywhere on the planet. But, I doubt the Germans armed any Poles with Mosins to any real extent. The Germans had a real dislike for the Poles, as did the Soviets.
It is way more likely that as an Iron Curtin Country after the war, Poland was in fact armed by the Soviet Union with surplus WWII rifles, hello........
The Soviets also had most of their union countries making guns after the war and is exactly why you see refrence to xyz AK or xyz Makarov, etc.
Jon, when you run into stupid combined with ignorance, it is way better to just walk away, before another clown observes the discussion and can not tell who is what. The old, "Never argue with a fool" axium.
Ed