What possible reason could you have to think that when it's EXACTLY like the door leading to the Dark Brotherhood. "What is the color of night" and "What is the music of death" is same question format and the same melodramatic poet style and it's a big black door with a skull on it. If the Volkihars are supposed to be unique, they should get a unique way of hiding that doesn't blatantly rip off the Dark Brotherhood.
Well for one the location seems very strange for an dark brotherhood sanctuary. The doors was according to the article placed very near a lake, and the Volkhiar vampires lives in caverns beneath lakes. Reason number two, we do not know it the skull on the door is an actual skull or a more "painted" art kinda thing like the one the dark brotherhood had in Oblivion. If its just a skull nailed to a door I highly doubt it would be a dark brotherhood sanctuary. And at last, talking doors or entrances has been done prior the dark brotherhood in Oblivion, its one password demanding door in Bloodmoon aswell. I really hope the dark brotherhood has its sanctuary somewhere else than by a lake. I like them to be more urban