Dreaming with a foot in the real world.
Ok, so, this pilots sleeps as he is permitted to, but have you never experienced dreaming about things that happens around you? Audition is the sense that used to wake us up over the presence of a predator. In emergency first aid, they tell us to yell loud a victim's name in order to try to bring back an unconscious patient. (along with other measures including inflicting pain) It is understood that audition is the last sense to switch off when you sleep and when you sink into a coma.
AC SOPs indeed says a pilot can't touch the controls 15 minutes after waking up from a sleep period. Could this pilot have heard the com chat in its integrality or just his co-worker answering control about the incoming plane? I can almost then get into his dream (like in the movie Inception) that he is at the controls and for reasons that only happens in nightmares, he can't get out of its way. The plane either doesn't answer his commands or the other plane matches his every moves. He wakes up, still somewhat dreaming (hence the rule) and instinctively, for self preservation, he takes controls to continue trying to avoid the non-incoming plane. Can we even call that some form of somnambulism here?
Anyway. To me, this incident illustrates more the indiscipline of passengers when you tell 'em to buckle up. As a SLF too, the thing I fear most when I fly, is getting a 90Kg person in my face.