Other objects
It was not just bodies wearing clothes that were found with these mummies, there were other objects as well next to them. Objects had to have been transported all the way from the distant coastline and carried on top of a mountain. That is a lot of work and effort to put into a human sacrifice.
The objects were things like pottery, headdresses, and other artifacts that came from all corners of the large Inca Empire. At that time, the Inca were at the height of their power in the region and were dominating the entire area of their vast empire. So they took their sacrifice very seriously.