Boid developers have revealed that the muting feature of the app is being reveamped. An improved version would be made available in a future build.
Mute feature is very useful on a mobile Twitter clients. It specifically comes handy during live events and other instances where there are massive number of tweets with similar keywords/hashtags. Users not interested in such events can mute them to avoid getting spammed on their Twitter stream.
Here is a screenshot of the improved user interface: