Translation:He made a nut cake with chocolate.
Is a Nusskuchen a particular type of cake? I've never heard an English person just say "nut cake". Maybe walnut cake, almond cake etc.
There's plenty of recipes here: https://www.chefkoch.de/rs/s0/nusskuchen/Rezepte.html , so it is a term for a class of cakes which use nuts as ingredients, yes.