We are having many users signing in (oauth) reporting issues where they email is not valid. Problem is that they do not have an existing account, but message displayed is very confusing.
It should do the following:
Thanks for the improvement tip - we may consider it as a future request. However, this question is not relevant to SO - please use in the future Uber google groups (https://groups.google.com/forum/#!forum/uber-developers) or send post's on Twitter at @UberDevelopers or @Uber_Support.