Great-great-grandfather emigrated from Bohemia to Berlin around 1870-1880

I’m still sorting this out and I appreciate the feedback everyone here offers.

My great-great-grandmother was born in Bavaria and moved to Berlin at some point around 1870-1880.

My great-great-grandfather was born in Bohemia (Unterlohma) and moved to Berlin around the same time.

They married in Berlin in 1888.

From this I assume my GGgrandmother was likely German, but lost that and was considered (today’s equivalent of) Czech when she married my GGgrandfather? But he would’ve lost any Czech claim after 10 years in Berlin. As far as I know, he never officially applied for German citizenship, but I don’t know how I would find out right now. Would that have made him stateless? The next two generations were born and lived in Berlin until my grandmother emigrated to the US in 1925 as a child.

I thought I read somewhere that people living in Germany before a certain date and for multiple generations were considered German? Or am I remembering wrong? Or does it all hinge on whether my GGgrandfather formally applied for German citizenship?

Thank you everyone for all of your help and patience! This has been a fascinating rabbit hole and a wonderful chance to learn my history!