This could not have happened if the individual was heated solely by pyroclastic flows – high-speed currents of gas and other volcanic matter. The temperature of these flows from Vesuvius would not have reached higher than 465°C and would have cooled too slowly.

Ok, so ignoring how that’s pretty low for a pyroclastic flow, I’m pretty sure the evidence for the ash arriving first is the bodies that were encased by it. If the pyroclastic flow hit first, I don’t think any of the actions the people were found in would have lasted long enough to be coated in the preserving ash.