Thanks for clarifying, glad to be wrong about this one. Would you happen to know if this was true at some point?
AFAIR to choose your major you'd to fill a list of preferences - priority of majors in different IITs. These are then awarded based on merit - rank in the JEE(Joint Entrance Exam). So if you want a specific major at a specific IIT you'll have to get higher ranks in the JEE.
This has never been true; for the past 40 years, at least.