Ok, I will try this.You are using Bukkit's CommandExecutor and you are returning false.
Returning false in a onCommand will send the 'usage' you have entered in plugin.yml.
Returning true should fix the problem.
In other words, false means the command has "failed", and true means the command has completed successfully and the correct usage of the command should not be sent.
Or, just completely remove the 'usage' field in plugin.yml.
