The hub firmware version and database have always been separate--the backup you can download from the hub (or store in the cloud with the subscription) contains the database, not the firmware, and the database contains things like installed apps and the hub device list. The firmware, of course, must be done via either the Settings page (to upgrade) or the diagnostic tool (to roll back to any of the last few you've had installed).
It's usually a good idea to match regardless, but in this case they're very clear that it does matter: if you roll back the firmware (and have Rule Machine installed), then you should also restore a matching database. There are no checks in place, so it will let you roll back without also restoring a database or restore an older/newer database to a hub firmware version that doesn't match. Usually this is harmless; this time it's not, under this specific condition. (Every once in a while there are breaking changes; I can only think of a few in the past, so this is just another one of those.)