That would be expected were the enemy not sending its passenger jets hoping to trick us into shooting it down. Modi’s IAF is a tool of his political plans. Should our radar pick up an enemy return or several close to a civilian airliner on the same route this spice jet was taking, what would our Air Force do. (Enemy fighters flying just under a civilian airliner)
As you stated, We would be forced to declare it hostile, and be forced to intercept it, if not engage it from BVR range. We would be hard pressed to present evidence to the world if we mistakenly shot down that airliner as stated in the media piece.
An IRST gives us visual confirmation (it might be required depending on our rules of engagement in the current non-full war state) and provides with visual evidence in the event we need to show the world what we faced, and that India caused the situation in the first place; a picture is worth a thousand words.