For triggered tasks, the username field will show the user who created the task, the pipeline actually runs as the task owner. A change to show the task invoker username was done a few releases back. It is displayed as a new property called Remote User
in the pipeline runtime info dialog, under the Extra Details tab. If the task was invoked with basic auth, this property will show the invoker username. If the task was invoked with some other authentication, like bearer token, this property will not show up, since we do not have the invoker details in that case.