The exception that proves the rule is from a legal argument by Cicero.
It means that if someone bothers to write an exception in a law, say e.g. "but in case window is broken by stone smaller than 1 cm in diameter, then it's the owner of the window that should pay reparations", then in the general case it's likely the thrower of the stone that pays, otherwise there would have been no point in adding so specific an exception.
This is the correct answer. "Exception proves the rule" = a documented exception is an evidence that a general rule exists.
When you see text "kids under age of 3 years don't have to pay", you can conclude that older people are supposed to pay.
The analogy for Google situation would be if hypothetically someone found an internal e-mail written by the boss of Google HR department saying "contractors who have relatives in Google, or who have published their story on Hacker News front page, need to be fully paid for their work". Then we could conclude that other contractors typically don't get fully paid, even if there is nothing in the e-mail saying that.
It means that if someone bothers to write an exception in a law, say e.g. "but in case window is broken by stone smaller than 1 cm in diameter, then it's the owner of the window that should pay reparations", then in the general case it's likely the thrower of the stone that pays, otherwise there would have been no point in adding so specific an exception.