The post admits this, first in the summary: "However, Burning Man’s near zero death rate over its existence is abnormal, and likely due to selection bias of healthier attendees and other confounding demographic factors".

Then again in the final sentence: "The more likely explanation for the remaining gap is something no demographic slicing can capture. Burning Man selects for healthier people who are willing and able to spend a week in the desert heat, regardless of their age, race, or income bracket."