I think anyone can make this kind of cover by affixing proper postage and asking for hand cancellation.!!
We had seen some 1948 Gandhi stamps used abroad from Tibet as well as Nepal. To me both looked like forged because it has lot of known issue such as date of Sunday used on cancellation as well as there is no genuinely used of 1948 on official first day cover.!!
In past I wrote blog post about India used abroad stamps. Following are the links.
Gandhi stamps club.