They said: ". . . from an IP address not associated with an Uber employee and otherwise unknown to Uber . . ."
Taking them at their word, if they don't know, how do they know it was not associated with an Uber employee? Just because it wasn't an IP address assigned or controlled by Uber doesn't mean an employee couldn't have used a Proxy or a computer not associated with the Uber network.
Any judge with even a smidgen of tech savvy would laugh the suit out of court based on that alone. Given that they "believe" the GitHub post contained a key, the entire thing is nothing more than a fishing expedition. Where is evidence - amounting to proof under Rules of Evidence - that this had anything to do with GitHub? Or that a "key" was ever made available on the site? More likely an employee had possession when he or she walked out, er, drove out the door.
As I said, any Judge not willing to be laughed out of court would laugh the suit out before he or she becomes a part of the countersuit.
Logic is a bitch. If A=B and B=C, then C=A. I wonder how many judges passed their logic classes? Or even took one?