It's part of specially provisioned Dedicated freight corridors: https://en.wikipedia.org/wiki/Dedicated_freight_corridors_in_India. Currently 1 is complete and another is underway, of 6 total planned. I don't think (but am not very well across Indian railways news) that the double-stack would be rolled out much further.Doubly impressive in that they have sufficient clearance not to need well wagons.
India's railways have been seeing lots of investment in recent times, both with metro networks in the cities and things like re-gauging and electrification projects on the wider network. Project unigauge now has 96% of the network on broad gauge, from a starting point of 46%. And their high-speed network (standard gauge, interestingly) is rapidly developing.