Did they forfeit them? Or had they vested and in anticipation of IPO likely exercised either all or nearly all of their options and then sold post-IPO?
Before the Susan fowler thing they had a rule that you had 30 days to exercise your options after you leave or separate as they called it. Since the company's value went up so much most people couldn't afford to pay the tax and because it was private you couldn't sell it (employee lock out is in November). Lots of people were handcuffed because of this, and I know a few that walked away. After the Susan Fowler thing they changed the option thing to like 7 years.
With 4 years of tenure they should have vested much of their stock, but I'm not sure when Uber started doing grants rather than options. If they had options they may not have had the cash to exercise.
I think they moved to RSU's in mid 2015 or 16.