My Grandpa was born in Poland in 1939, and he told me that he remembered the soldiers(when he was 4 or 5) and said that the Germans left chocolates and were nice. And in fact his mum usually cooked for them. Then he said when the Russians came they where animals. One of them apparently hustled his mum.
Was this true throughout German occupation or was my Grandpa and his family lucky with the Germans that came his way?
While I won't hand-wave away an individual story of (what I'm assuming to be) a child receiving kind treatment, these types of stories pop up a lot, and it's important to remember that the German occupation of Poland resulted in approximately 22% of Poland's pre-war population dying as a direct result of Germany's occupation due to genocide, disease, starvation, relocation, forced labor, and other acts (https://books.google.com/books?id=RnO_Z3y5elgC&pg=PA175#v=onepage&q&f=false). The overall design was to destroy or relocate as much as 20 million Poles (much more than a majority of the population) to create "Lebensraum" for the German people as part of Generalplan Ost (https://web.archive.org/web/20111125231946/http://www.atsweb.neu.edu/holocaust/Hitlers_Plans.htm).
It's certainly worth noting that survivor bias is real. I'm again only assuming your grandfather was a child, but it would make sense that if he survived, it was likely he'd have either an extraordinary or surprising story based on his circumstances. It's certainly believable to find stories of people receiving kindness in the face of such adversity, but it's one story in an album of literally billions. In such a far-reaching conflict, it could be just as likely that other people had the same experience, an opposite experience, or a totally positive or negative experience with either country's individual soldier. I don't deny that he could have met a kind German soldier, but given the figures presented, I'd say it was not ordinary and should not color one's judgement beyond examining the individual level.
Don't think I take the USSR's overall acts lightly. It's also worth noting that the USSR certainly treated Poland abhorrently, either in its 1939-1941 occupation or post-war. The occupation in 1939 saw the Soviet government committing war crimes, execution, torture, forced relocation and labor, political re-education, and other travesties, but incomparable (not inexcusable I really mean that they are two completely different monstrous acts in terms of scale and goal) in so many ways to Nazi Germany's design on pure genocide.