I think the sociopathic element comes from the lack of empathy and remorse displayed by AF when he was in the police car. It's obvious enough that it is antisocial behavior to stab a friend to death. His behavior upon capture does suggest a sociopathic tendency. A selfie in the police car and smugly asking if "anyone has seen Tristyn lately" is a reliable indicator of antisocial behavior.
If some evil impulse had overwhelmed AF and he lost his mind for a moment, if he didn't have sociopathic tendencies he would have been sobbing, apologizing, or making excuses such as he feared for his life around Tristyn.
The Macdonald Triad makes some sense, IMO, but it is not universally accepted. Bedwetting, in particular, may cause a child to be angry and frustrated, but is not in itself a violent act like animal abuse and pyromania.
IMO the Zoom conference is a moot point. He was instructed how to behave to minimize the trouble he was in. It's the murder, the overkill, and the smirking lack of remorse that is very, very troubling.