ESO doesn't use a traditional "item level" system to make same-level items vary in power. Instead, there are actually hundreds of different quality types that fall under each of the familiar 5 colors. For instance, you'll find that world drops are less powerful than boss drops with the same quality and required level.

We are only generating the values on the tooltip based on if the items dropped in the world. The stats may vary if the item is not a world drop. We are currently testing better ways of letting you explore this data.