lives in NJ, works in NY, what is the tax rate on salary?

I'm using TT to calculate my son's tax. He lived all year in NY but worked all year in NY. This seems like the result (rounding off numbers):

NY took 26000 in tax on salary

the NJ tax on that salary is only 22500 so that's the credit that NJ gave for the 26000 paid to NY

 

My question is what happened to that 2500 paid to NY? Does NY keep that? If so, then in effect, he's paying the NY tax rate on salary and there's no advantage to living in NJ. What am I misunderstanding here?