In most cases, including yours, it doesn’t matter. Why? Because you don’t declare your major when you start as a freshman at the University. You have to take a variety of prerequisite classes before you can declare your major and enter into a department (for A&S this usually occurs sometime during your sophomore year). So in your case, yes you were accepted at Pitt now you can focus your schedule around completing all of the pre-req classes to declare into the CS department.