99.95% is correct, but the Compute Engine SLA is actually here: https://cloud.google.com/compute/sla
Today's incident did not impact App Engine at all.
(Disclaimer: I work in Google Cloud Support.)
This allows unlimited small outages:
"Downtime Period" means, for an Application, a period of five consecutive minutes of Downtime. Intermittent Downtime for a period of less than five minutes will not be counted towards any Downtime Periods.
That is like 17 of such 15 minutes breaks per year, i.e. an allowance for one small (or a large fixed quickly) screwdup/month :)