It may be a stupid question but if I applied ED to NYU and only made my second choice major, am I still legally obligated to attend?
Yes. An ED acceptance binds you to attend NYU, regardless of the major/school you’re accepted into. You don’t declare your major until sophomore year anyway, so the major doesn’t matter, and you can transfer internally within NYU to different schools.
No, you are not obligated to attend if you do not get into your first major. This can be found in the NYU section of the Common App.