The amount of his federal gross income is initially important only to determine whether he has to file a Maryland return.  States use two different methods for figuring tax on nonresidents.  In some cases, the more total income, the higher tax rate on the portion earned in the nonresident state.  In other cases, the tax bracket is the same whether the income is five figures or seven figures.  

It's been a while since I have done a Maryland return, so I don't know how their computation works.