My post was in response to the OP questioning if it could have been different from a targeted one person killing plan. I thought it was an interesting question. We really don't know for a fact at this point where BK started, 3rd vs 2nd floor. He could have encountered Xana upon entering, as we know she was up receiving DD and on TIKTOK, which meant a surprise of Ethan being there.
I mentioned BK may well have been targeting one roommate, but was also prepared to kill whomever became an obstacle. Agree, Kaylee sleeping in Maddie's room would likely have been another surprise, whether he was targeting Maddie or her.
I believe after murdering Maddie, Kaylee, Xana and Ethan, he felt he needed to get out of there ASAP (dog barking, neighborhood noises). I don't think BK saw DM, she said he observed him from a couple of feet away. If they had literally come into direct contact, I believe she would be dead as well.
I did say I changed my mind daily, lol, but it's a good exercise to consider all possibilities. IMO