I think the likelyhoood of two incidents happening in the same period is not astronomically small, and is a variant of the birthday problem. It's a bit counter intuitive but if you have a few incidents during a year, the probability to have two incidents the same week is a lot higher than what you would expect.
The birthday problem involves random people with unrelated birthdays. This is like two not-random siblings both calling in sick in the same week. The case of two large Google outrages where the whole service gets conked has much more potential to have a shared or related cause than two birthdays happening at once. You're right that it's not astronomically small, but the odds of them being related seem healthier than the odds of them being unrelated.
https://en.m.wikipedia.org/wiki/Birthday_problem