Yes this is very very very confirmed. I killed the lesser spire spirit in this spot over and over and on the 6th spawn this guy showed up. The spawn time is 12 minutes and the coordinates 202,555 are right. Thanks very much for posting whipcream, that info saved me a bunch of time.
The Dusty Spire Spirit spawns at loc 202,555 near the bottom of the stairwell. His placeholder is A Lesser Spire Spirit. We were keeping the cave clear and he always spawned at this location.