Great to hear you are using that interface. The username field was added when I first designed the interface with the intention that when we had the user information at the database level it could be added to the notifications. The way the eventnotification interface works is that it makes use of our configuration engines notification stream. It's the same way the TMM can find out about CLI changes immediately. So, when a user makes a change it's audited and then the value is saved to the configuration database. But, as of now, the information that is saved doesn't include the user that triggered the change so the configuration engine doesn't have the username to be able to send back out in it's notification stream to the listeners which include the EventNotification daemon.
Probably more than you wanted to hear, but hopefully we'll have the audit information in there in the future, but it's not there now.
-Joe
Nimbostratus