Kashubians are a distinct ethnic group, who preserve their own unique culture. They also have their language.
Of course, among other Polish groups there are differences too, Poland is a bit bigger than Liechtenstein, so obviously the differences used to be visible. Even nowadays I was told that I speak a bit differently, by someone who’s from Warsaw.
Sometimes when I think about the Kashubians from historical perspective they are the descendants of the Pomeranians. Since for some time they were living in Prussia, obviously some germanisation took place, like russification in other parts. But most of the Kashubians when asked about self-identity they mention Polish nationality, and Kashubian ethnicity.