Varian had heard the HOWL and that was enough to get him racing to the door of the house. Something bad was happening and he's terrified someone he cares about is suffering. He can feel the PULL of the bond- and even if he didn't have that, his tattoo letting him know where Luz is means he knows exactly who the creature that's tearing out of the house.

Naturally, he runs after her. She didn't think twice about doing the same for him when he'd turned, and he doesn't think twice now. Of course, she's got more legs than he has right now, but he's doing his best to keep up.

"Luz?! Luz wait!"