The physiological changes led the way — and we adapted our methods and tools to match. To suggest the reverse is just semantically adjusted Lamarckism.
Without fire and tools, those with weaker jaws could not survive. Fire and tools allowed more to survive, and strong jaws no longer needed to be selected for.
I would go for fire and tools preceding physiological changes as these would lead to an adaptation to the lesser stresses rather than those associated with tearing raw meat off a carcass, chewing tough uncooked food, the grinding wear of working leather by the mouth.
With fire and tools, the smaller jawed individuals could survive along with the stronger jawed individuals. The stronger jawed individuals may have lived shorter lives showing off their strength by wearing their teeth out sooner thereby leaving the gene pool.