To be fair CA's blog post also mentions internal conflicts between the Dragon siblings, chaos cults and an invasion by the Monkey King (monke dlc confirmed!!!). When the Polar gates collapsed and the Old Ones fucked off then he united the tribes to fight chaos. I read the whole unite the tribes things as the Dragon Emperor was chilling in Cathay before the Old Ones came and he continued to do that while they created the different species. Well since GW is finally writing 'specific' lore for Cathay and introducing them as a faction they're within their rights to change/keep whatever they want from the old lore.
