Again: the forum content (= data) is stored in the database.
That database is accessed using the credentails in your config.php
If database backups were made using the phpBB backup feature (in the ACP) then these are saved in /store.
If database backups were made using other (external) utilities (phpMyAdmin, Adminer: the 2 most offered by webhosts) then these are stored in a location decided by the user at the time of making the backups.
Basically , with a database backup it is possible to restore a board providing
a) that the database backup is complete and not corrupt
b) you can recover the phpBB files of the same version
c) you can recover the extension files which were in use when making that backup (without the files it may still be possible but it's a very tedious job)