Isn’t this area considered the old East Prussia?
I don’t believe so. Silesia is down closer to Bohemia (Czech Republic) and other former Habsburg (Austrian) dominated lands.
Prussia (and later Germany) was one of the players in the game to dominate Silesia, however.
Silesians speak german, czech or polish...depending on which country they live in. Prussian was spoken in the regions of Masuria, Silesian I seem to remember was a part of Bohemia.