Need help understanding how to calculate Nonresidents taxable %

If you receive rental income from a state that you do not live in, are you supposed to pay taxes attributable to that state?  I was told no.  Nonresident Schedule PN to fill out.  Column A tells you to include all income from all sources.  Things like wages, salaries, taxable interest, taxable dividends, alimony, real estate rental etc.  There is an associated Column B that says "amount of Column A attributable to state"  Since that client does not live in that state, they have 0 for wages, salaries, taxable interest etc.  They only get rental income.  Let's say total annual rental income is $10,000 from all real estate rental income.  Let's say amount of real estate rental income for this particular state is $4,000. 

 

So would Column B be 0 or $4,000?  I can't imagine client pays nonresidence taxable 40% of their AGI, then multiplied by that state income tax %, as tax due if they only had rental income.