There can be 3 reasons why you see boards from others coming up.
1. When you logged on you were automaticly added to watch and listen to the ongoing broadcast of an event.
A: You can close the live broadcast (audio and board) by going to the menu above in BlitzIn. Click on Broadcast and then click on Close live broadcast.
If you still have an older BlitzIn then it can be that the option for Broadcast does not exist in your menu. You then need to type 'unfollow' on the command bar of your Main Console. To stop the entire broadcast (audio and board) you type instead 'tell webcast nofollow'.
2. You clicked on a follow option for a certain player or type of game.
A: Go to your Main Console and type there on the command bar 'unfollow' as shown in picture above.
3. You typed or clicked a follow command for Simulbot.
A: Go to your Main Console and type there on the command bar 'tell simulbot unfollow' (for Main Console picture see above).
For more information on follow and unfollow you can read the ICC helpfile "help follow" .