What is the date of your travel ? I saw the higher fare between 11/7 to 19/7 is around 156000 INR (around US$2250).
If u book CJB direct to SFO, there are lite fare available, thus it is cheaper.
If u book via multi city, there is lite fare available for CJB-HKG, but only standard/flexi fare from HKG-SFO. And for multi-city, no mixing of fare types. So all will be under standard fare which is higher.