The missing status page [1] treats it as downtime any time any component of the system is down, and calculates the overall uptime based on the time that doesn't overlap with any individual category outages, and the overall downtime as any time overlapping with at least one individual category outage to avoid double-counting They show 24h of minor outage on that date.

I'm guessing that this site is taking the downtime in a given day across all services and adding it up, which would mean the worst possible day has 10 days of downtime (a day of downtime for each major category).

1: https://mrshu.github.io/github-statuses/