It depends what they’re looking for. They might want to see the “whole” of his income Federally to see how that activity relates to his activity in NY. They might want to verify the starting point of the NY return which is typically Federal Taxable Income.
But again, remember that politicians generally turn over only their 1040s. Even Mitt Romney never turned over anything other than that. So this is unprecedented that his business returns are on the realm - if indeed they are.
And as I say, if all they are getting are his 1040s, they’re not going to find out much. (other than maybe he was cheap with charity) :)
When I worked in New York the accounting software was set up to have all the tax returns — Federal, NY State, and NYC — linked together. I can’t imagine that any accountant would sign off on a return with even a small discrepancy between what was reported to the IRS and what was reported to the State.