Amend only state return only; however, 1040X got generated

I need to amend my state return to claim credit for tax paid to non-resident state.
I followed instructions in
https://ttlc.intuit.com/questions/3222522-can-i-amend-only-my-state-return
However, turbotax generates 1040X and asked me to mail it to Federal and State.
I don't understand why I need to amend my Federal as the change is related to my state only.