"No, the inhabitant is not a citizen."
Translation:Nein, der Einwohner ist kein Bürger.
If I understood this link correctly, "Einwohner" is the person who lives in a specific country, city, state etc. "Bewohner" is the person who lives in a specific house, building etc. So one can be an Hamburf "Einwohner" or a "Bewohner" of that red house.
Sein (bin,bist,ist,sind,seid) do not make the predicate accusative or dative. The noun stays nominative on both side.
Also, der becomes dem in the dative form, so if it had been dative you would use keinem, not keinen.
The accusative form is where der becomes den and you would use keinen.
When you use the verb sein (to be), you are essentially equating the predicate noun to the subject so they are both nominative. That's why people say "this is she" instead of "this is her" when someone calls on the phone asking for them. (Not everyone does do it, but it is technically right.)