I just remove and reinstall wpForo, I have the same problem. After reinstalling, wpForo has keep all my settings, this is not normal, however, before reinstalling wpForo, I clean the database after deletion)
there is really a problem with your plugin
It seems you've clicked on Disable button, not on Uninstall button. If you uninstall it, there is no way to keep the same settings.
here is a screenshot of my database, are there still wpForo tables? (I see that there are still buddypress tables, yet I uninstall)
There is no wpForo tables in your database. And I don't understand why you ask about BiddyPress tables. wpForo doesn't have any relation to BuddyPress tables. I've not asked you remove buddyPress tables and wpForo doesn't remove those. wpForo only removes its own tables. BuddyPress is not wpForo plugin.