User blog comment:Shermoen95/Pantheon and checklists./@comment-4636093-20121224042947

It's not just a passive of that skill though, in fact it doesn't actually do anything for the skill it's gained by. Instead it benefits his auto attacks and his Q.

It can't really be counted as a passive of his E, rather than a secondary innate passive. So that's why it isn't named as anything to do with his E.