I'm not sure. Xaar isn't an official source; his knowledge about bosses comes from using the map editor. In some cases, he even relies on rumors (Shadow_Elemental, although listed under "bosses," has the appearance of a regular neutral creature, and its model is exactly the same as the neutral shadow_elemental. It's likely that the developers initially planned for this to be a boss, but then turned it into a regular elemental, leaving the resource where it was. There's a lot of this kind of "junk" in the fifth game). So, until we get information from the developers or uncover the campaign storylines, I don't see the point in posting this.
P.S. Kosh, I think these two messages should be moved.