I have a 1099-NEC from a summer camp I worked in MA. I attend college in NY and work a small job there. Why is NY claiming my summer work wages and taxing them too?

New York taxes all of your income no matter where it is earned. They then reduce their tax rate on that income to compensate for the percentage of your income earned out of state. So, even though all of your income is taxed, it is taxed at a lower rate than if you had earned all of it in New York.