This is possible, but:As I was writing the above post, it struck me that BK surely must have thought that KG and the dog weren't there. I know that's old ground but he must have had a gap in his info - maybe last he heard was that KG had left town to relocate and work after finishing studies. He maybe thought M was alone in the upper part of the house and that he had a sufficient watertight plan to control her on a 1:1 basis, plus a potential escape route in case of trouble, imagining that anyone lower down in the house wasn't a problem. If he's a control freak and planned this incident, a dog and a second person, possibly with their boyfriend in tow, would be unmanageable variables.
Even if he originally thought KG wasn't going to be there, once he made those three passes in front of the house, he would have seen the extra car parked there. He probably would not have known it was specifically KG, but he would have definitely known someone extra was there. Even worse, that extra car could very well have been a boyfriend as far as he knew.
Also factor in Ethan's car being there, and the DD delivery, and you have a house with a very high likelihood of people being awake and guests being present. It's a very bold move for a killer to have gone in regardless of this.
As I have said before, my only idea as to why go into such a high risk situation anyway is because it was the last night before snowfall.