The end result seems to have been the intentional desecration of the corpses of a previous ruling dynasty in a massive, public bonfire, and the (probably intentional) use of the undifferentiated remains — jewellery, precious beads and more — as construction material.
With the other terminal classic period fires maybe we can suggest that there was a change in political power across the Maya world and part of that was burning the old dynasties literally and figuratively as described here.
That's because it's an illustration of a different altar, #12. The picture is of Altar #13. Both depict the same ruler, which is why they're in the same figure.