Genealogy /
THE MEANING AND RESEARCH OF MY POLISH LAST NAME, SURNAME? [4500]
BIEŃ: from Benedykt (patronym) or locality incorporating it (toponym); some 4,500 users in PL; no connection to French adverb bien; Benedyktz ah spawned a plethora of surnames including Bieńkowski, Benko, Banach, Banaś, Banasiak, Benedyktowicz, etc..
STĘPIEŃ: someone who married into an inheritance.
The Poznań connection is explainable. As a matter of principle the old Polonian immigrants would give the name of the provincial capital when asked where in Poland they were from. They figured no-one in the USA could possibly have heard of Pcim Dolny or Kozia Wólka so they said they were from Kraków, Warsaw, Białystok, Poznań, etc. The former Großherzogtum Posen (Grand Duchy of Poznań) bordered Prussia which included Pomerania (Kashub country). Perhaps your ancestor had lived in a border area between the two. On the other hand, he may have been born in one place and identified with his Kashubian roots till his dying day, but later had to move before coming to America.