You have to understand that BuddyBoss works on the basis of BuddyPress and offers 2 different things:
- The BuddyBoss theme
- The BuddyBoss platform
The latter is free and actually includes BuddyPress + BBPress, so 2 plugins in 1.
To get to the point, the theme only improves the appearance of the BuddyBoss platform plugin and the performance of the site. This allows you to have an updated site unlike other sites that use BuddyPress.