It's possible. I believe he had to strip off the clothing at some point, but it sounds like when DM saw him, he was still clothed (and heading in the direction of the slider). In that case, he must have paused in the kitchen or the living room to do so, unseen by DM but seen by BF (who up until this issue, had apparently been sleeping downstairs on the first floor).
I believe he needed to stuff his things in a plastic bag or duffel or container before getting in the car, at any rate. If he didn't, there should be some blood traces in the car. OTOH, he did kill 3 of his victims while they were under covers/on a mattress and he didn't slash any necks that we know of (so possibly no arterial blood spurt).
OTOH, maybe he is far more disorganized than I had thought. Maybe he strips on the deck, realizes he forgot the sheath. dashes back in, is seen by BF, runs out without the sheath. Maybe he didn't plan anything to protect his car.
IMO.