Elon can't have this both ways, though. Tesla has disclosed that it will use social media for financially material announcements, and Elon has embraced this. It can't be legitimate most of the time and illegitimate when it makes for a convenient defense.
Personally, I don't think Elon's intention was to defraud -- I think he was impulsive and careless, and I expect the SEC will reach the same conclusion. But I think if he's going to use Twitter to talk about such things, his tweets need to carry the same weight as an equivalent SEC filing.