My feeling is that the difference between Dorf and, say, Kleinstadt, or
Staedtle (it's called that in the South German dialect, with which I'm
familiar, and probably other areas too) was mainly in the type of
livelihood of the inhabitants, at least in Germany. Since a lot of Poland
was German-speaking for many years, that might well have been the case
there, too. A Dorf would be a rural village -the majority of the people
would work on the land. A Kleinstadt might have some industry, but would
also tend to be larger in size.
St Albans, UK.