>>11857310
Ah, you missed it...
This is actually marrying the old character profiles that call Chaos a mutated Chao. (Presumably, this is because in the JP DC release, he actually made a Chao screech in that scene where he appears in front of the echidnas advancing on the Master Emerald - this was removed in later versions.)
What Frontiers adds is that the Chao are a result of the ancient aliens assimilating into the local wildlife, better explaining Chaos' mutation - he resembles the ancestors of the Chao. Oh, and the Chaos Emeralds were originally from another planet, attracted to the Earth's Master Emerald.