Search opinion needed

LBartsch

When looking at death, US census and immigration records for my g-g-grandparents, I've noticed that my g-g-grandmother and her children are always shown as either from Kurnik ,Posen or Poland (essentially same place). In these documents, my g-g-grandfather is always shown being from Germany never anywhere else.

1. Is it safe to assume that my search for my g-g-grandfather should be anywhere but Kurnik ,Posen or Poland since Germany is specified?
2. I am assuming that in the 1810 to 1820 time frame Germany was a loose confederation of autonomous states so the term Germany could refer to any of those states?
3. My g-g-grandfather's father was an Unteroffizier in the military and his last known residence at time of death was Bromberg. Is it safe to assume that he was in the Prussian army?

many thanks in advance for the assist