If the killer targeted one or more of the victims, how did he know their movements? How did he know they were home, or even coming home? Especially if the intended target was Kaylee? And how could he be sure that no one ELSE was going to come home?
He was already with K&M at the food truck and knew their destination when they left, OR was with X&E and knew their destination and time of departure, OR he was watching the house. If he was watching the house, I posit that he was watching from inside somewhere. I don't think he was sitting in the frigid trees waiting. Was he really waiting for hours in the woods, in the freezing cold, with no phone to keep him occupied? Risking someone seeing him? I don't think so.
I think the killer either lived within sight of the house and watched from home, or he crossed paths with the victims either at the food truck or wherever X&E were last (frat party?) and knew precisely when the victims left for home. But in that case he likely would need to be at least acquainted with the victims to know the house and know the occupants of the house. Because even if it is some random killer watching, and he sees them all go to bed, how does he know that other roommates or friends aren't coming by too?