How does Chris think the blank envelope ended up in his bathrobe?

Chris suspects that the blank envelope ended up in his bathrobe after he unknowingly picked it up while cleaning or organizing his space. He recalls a recent visit to a friend's house where similar envelopes were used, leading him to believe he might have accidentally taken it home. The randomness of its appearance makes him wonder if it was a result of being in a hurry or distracted during his day. Ultimately, he views it as a minor mystery without significant implications.