Nonresident New York State Taxes - Only a portion of income

Hello,

A small portion of my income was earned from a New York State source. I reside in Montana and work predominantly in Montana, so I'm a nonresident in NY. I worked a remote, paid internship for a company based out of New York City. When I go to file a nonresident state return with NY, TurboTax lists my entire federal income and shows that I owe NY state money.

On my NY W-2, it shows state taxes taken by both New York and Montana. It's a very small amount as it was only a 3-month internship, part time hours with relatively low hourly pay. I've never filed a nonresident tax return before, and do not understand why TurboTax would list my entire annual federal adjusted gross income for the nonresident NY tax return, when only roughly 10% was earned from a New York source. Could someone please give me guidance with this issue?

Thanks in advance!