I have a user get notifications for every ticket created or edited even though he is not the Assignee, Reporter or Watcher (these are the three rules in the Notification Schema). Why?
All recipients of notifications are determined in the notification scheme. My first thought when hearing about your problems is - are there any custom events in the workflow?
These custom events have their own recipients in the scheme (works exactly like the default events and is shown in the notification scheme if there is one). Make sure there are no custom events with your user assigned as recipient.
Hope this helps!
Good luck with your Jira endeavors!