Not the sharpest knife in the drawer
Elon Musk presumably hasn't yet quite worked out that this is a war of words only one side can possibly win.
On the one hand, anything Martin Eberhard says about Elon Musk has no implications for himself or whatever he does next.
On the other hand, Elon Musk's comment about Martin Eberhard begs the question "so, you're trying to sell us a car designed by the worst individual you've ever had the displeasure of working with?"
Whoops. Elon, open mouth, remove foot, then close mouth again and leave it that way.