Earlier quoted context omitted.
It's not a contest of who is more underpaid. This would indicate that Google systematically underpays, regardless of gender. THAT is the real issue here.
How likely is it possible for Google to systematically underpay? People voluntarily take positions there (and in fact, compete to get hired there).
I would say this makes it more likely for people to be underpaid, especially when factoring in hours worked. See SpaceX for another example.