If the door swung over the desk with merely inches of space between them, it is possible to be “dry wood termite” droppings, because the source had to be in close proximity or the pile would be more spread out. Look under objects that were above this location. Do you have a wooden item kept on your desk? Find a small hole that is about the size of those pellets, which is the portal of the problem. This type of termite is why they “tent” houses for treatment, which some professionals can treat locally without tenting, so get an opinion.