Here's GitHub's historical uptime graph (on which this chart is based), saying there was no recorded downtime that day, or in fact that entire month: https://www.githubstatus.com/uptime?page=40
Just dumping HARs from devtools from a status site that hallucinates 100% uptime when it has no data. For example, all GitHub services had 100% uptime in June 1996: https://www.githubstatus.com/uptime?page=200
The graph gives GitHub Actions 100% uptime before it launched to GA in November 2019. That factors into the average uptime for every month on the graph before that. It's fully horseshit.
We don't have enough data to confirm if it's over or under reporting. This sample size of 1 is enough to prove the data is not perfectly accurate, but it's not enough to prove a skew bias in the data either way.
I am making an assumption that if Microsoft saw a lot of false positive outages they would fix that, but might drag their feet if there was an outage that didn't get properly recorded (assuming it's automatic to begin with, it might be that a human needs remember to update it).
[1] https://github.blog/engineering/infrastructure/introducing-t... [2] https://web.archive.org/web/20181211191456/https://www.githu...