Wisconsin gross income is below the filing requirement

We are non-residents of Wisconsin but have an investment in Wisconsin that for 2023 reported $359 in interest income.  Our 2023 Wisconsin return (as compiled by TurboTax) showed a tax due of $21 on this income. We filed our Wisconsin return and included a payment of $21.  The Wisconsin Department of Revenue recently sent me a refund of $21 and said my Wisconsin gross income is below the filing requirement.

 

Why didn't TurboTax reflect this in my return?

 

Thanks for the help.

Ken Templin