Fact 1: Mahan Air is owned by the Iranian Revolutionary Guard Corps (IRGC)
Fact 2: Mahan air is known to use its aircraft for sanctions busting activity, moving weapons and other banned goods.
Who benefits if a plane full of Iranian contraband lands in New Delhi and it is revealed what it was carrying?
New Delhi attempts to divert this plane away from the city. Why? IGI airport is sufficiently outside the city, and you have the same threat to civilians in Jaipur and Chandigarh, too.
Call came from Pakistan. A hoax attempt to have this plane land in Delhi? Did the call come from a number in Pakistan, or through official channels?
Once again: who benefits if a call seeming to originate in Pakistan makes an airplane land in New Delhi, an airplane carrying certain special goods? (Don't think just weapons, broaden your thought.)