“Another way of phrasing the above is that data consistency is not something that rsync can in any way guarantee.”
Rsync splits each file into blocks sized at the square root of its length, checks a cheap rolling checksum, and only computes the expensive hash on a match. It is clever and fast. It also makes no promise that a file changing mid-transfer arrives intact. If your backup script rsyncs a live database, you have a copy of something, not a backup.