Seems he would've or at least could've been tracking his delivery driver, and knew when he stepped outside that the arrival wasn't imminent. I wouldn't find it mysterious that he choose to wait outside; there are a lot of reasons one might opt to do so. As for not caring, it appears his roommate did announce when he was going to bed, and Caleb did tell someone he was going outside to wait for his delivery. Whether that was the whole truth or not, I don't think anyone knows yet for sure, but to me, it indicates at least some level of caring/sharing of info between them. JMO.
ETA: by "cover" I mean he had an excuse to be seen/heard going out the door so nobody would wonder or come to investigate; they'd be asleep or back to sleep whenever he decided to return. Had Caleb returned (after receiving his delivery OR after a quick meet-up with someone), nobody would've been any the wise.