Hey Pauly, your users are probably not gone. What most likely happened is the fresh phpBB install created a clean phpbb_users table with just Anonymous, and then your SQL import skipped it because the table already existed.

Open your backup .sql file in a text editor and search for phpbb_users. If you see INSERT statements with your usernames in there, the data is safe. Just drop the current table and reimport that part:

DROP TABLE phpbb_users;

Then paste the CREATE TABLE and INSERT statements for phpbb_users from your backup file into phpMyAdmin and run them. That should bring everyone back. If the .sql file doesnt have it, check the phpBB backup you made from within the forum itself, that one usually includes all tables too.