pacman-mirrors makes no assumption on the mirror itself but relies on the information provided in [status.json].
The mirror service relies on the content of the state file which is present in four locations on the mirror - root and branch
If the state file content matches the file with the mother ship - the branch is considered in-sync.
The mirror in question is a cloudflare mirror.
A cloudflare website is a cache of a single website and you may have had a cache hit while the cache was changing.