Spoiler:
Not so amazing, huh?
But look closer.
Yeah, that's not quiiiite a felsteed. The texture and model are both different, being a recolor of the human horse mount with glowing eyes and hooves, and most notably, it doesn't have a gaping hole in its chest like normal felsteeds.
Another factor is that the person riding it is Deathguard Lundmark, who, according to WoWhead has a physical-based shooting skill, which is not something Warlocks can do. Its also important to note that Lundmark is later seen just on a skeletal steed, speculated to be the same animal, only further rotted.
So, unless I'm misinformed, this mount is unavailable to players, and is found on a non-warlock character. So, is this a goof? What a well-preserved undead horse looks like? Is he to be assumed to be a warlock, or what?
What is this horse, and what does this mean lore-wise?
Also, can we have it? its pretty. (Ok, that's for another thread on another subforum, but still)