Okay, so you’ve successfully upgraded to WPMU 2.8.3.
Did you finish the WPMU upgrade by logging into the backend as the Site Admin and going to “Site Admin > Upgrade” and hitting the “Upgrade Site” button?
After that, you go to Plugins menu group and under your BuddyPress plugin, it should say:
There is a new version of BuddyPress available. View version 1.0.3 Details or upgrade automatically.