The first line refers to the final bonus you get when you turn in a completed leve.

It was the second line in that paragraph which seemed to hint at being an exclusive bonus to leves and crafting.

Quote Originally Posted by Rukkirii View Post
While this bonus will not be applied to quests and leve rewards, it will be applied to experience points earned during leves and crafting normally. When the bonus is saved up, the experience points you earn will be increased more than if you could not use guardian’s aspect. We will be introducing the specifics on the rest bonus on Topics soon.
Guess we'll have to wait for more info...