What guide is this for? it’s an important bit of information to give if you want us to look in to this.
I’m guessing Dark Iron Dwarf guide, but that guide does not have Horde quests because Dark Iron Dwarf is alliance.
Then again, can you name the quests this guide is allegedly telling you to complete that’s Horde?
It may be very well a bug, without any further clarification there’s not much else I can personally do.