Title and plates from two different states?

Hi all! I'm supposed to go buy a vehicle tomorrow from a private seller. We are both from NY. We were talking about the transfer process and he began to tell me that the title was issued in Ohio and would require a notarized signature. What seemed weird to me was that his license plates were from NY. Wouldn't that mean he should have a title issued by New York in order to have plates from NY? Thank you!