His exact words to his mother are, "I'm gonna fuck off for a while, dunno when I'll be back, see you," while standing in the foyer with a backpack containing his favourite book and not much else. Since he never announces absences as short as a weekend, his mother correctly interprets this as meaning he will be gone at least several weeks, and hugs him. He hugs her back, walks out, and takes off as soon as he is out of sight.