First Declension Ending Difference?

I took Attic in college and what I learned was that the first declension noun endings for the eta subgroup were as follows (using english letters so hopefully it makes sense)

Singular Nom: n Genitive: ns Dative: n Accusative: nv

Plural Nom: ai Gen: wv Dat: ais Acc: as

I recently popped on the Great Courses Greek 101 on Amazon. In the 2nd lecture in the series he lays out the “First Declension Endings” of nouns. He doesn’t mention subgroups (he might later), but what’s tripping me up is that the dative pl ending he gives is nsi instead of ais. I’m unsure what to make of this. Is he teaching a different form of Greek? Ionic or Doric vs Attic? I’ve never seen this before so thought I’d come here and see if anyone out there has the answer!