They could even have done slow rollouts. Roll it out to a geographical region and wait an hour or so before deploying elsewhere.
It was ages ago, but from what I remember, the first day rollout did occasionally catch issues. It only affected a small number of users and the risk was within the tolerance window.
We also tested locally before the first rollout.
Not thay it exuces anything, just that this probably wasn't treated as an update at all.