If you don't want your games showing in there you can disable it on the Usb Loaders, but will record the name of homebrew channel or forwarder in any case
To disable it, on:
CFG Usb Loader -> Open the folder usb-loader and find the config.txt, write this in there:
write_playog = 0
This you disable the Wii Message Board update for all games, but will record the name of the Homebrew Channel or the Forwarder Channel (In other words, the channel you launched the Loader)
USB Loader GX -> Go to settings and find this option: ''Message Board Update'', disable this and save
Wiiflow -> I don't know how
Another alternative is to set the Usb Loader to go back to Homebrew Channel after you finish the game and press ''Wii Menu'' on the Home Menu when you pause the game with the Home Button
...
You can clean all data from you Wii Message Board, there's two options:
1 - Formatting your Wii
2 - With this method:
http://gbatemp.net/threads/clean-you-wii-messageboard-without-formatting.343719/
I never tried the second method and people don't recommend to formatting softmoded wiis, so, take your own risk