Keep in mind – Sentinel spies were sent to Quel’Thalas by the night elves in order to spy on the activities of the blood elves and sabotage them. And the one who was assisting them with knowledge on those sanctums was that very same dwarf - Prospector Anvilward.
He gathered information such as detailed maps of different strategic buildings in Eversong Woods or a diagram of an arcane sanctum sketched in good detail, accompanied with numerous notes, and delivered the secret documents to the night elves, who sabotaged a sanctum with the knowledge obtained. I’m not sure if you’re referring to the dwarf as innocent or not, or simply providing more detail to those events but if the former – I wouldn’t necessarily state that’s the case.
Also going with the Horde would had been more strategic for their kingdom, with closer reinforcements nearby via the Forsaken than any Alliance kingdom. The aid of the Forsaken along with the sabotaging of the arcane sanctums in Quel’Thalas from the Night Elves only solidified the blood elves agreeable partnerships with the Horde.