@ParadoxicalHippy I know this is an old thread, but I only just came across it, and thought I'd comment in case I can be of any help to you at all. I've had trichotillomania since I was 12 (I'm now 40).
I'm not a dermatologist, but that does look like trichotillomania to me. It almost always follows what's known as a "Friar Tuck" pattern, i.e. people pull from the crown of the head, leaving the hair around the sides of the head intact (google "Friar Tuck trichotillomania" to see what I mean). In the first pic you posted, I think it's also possible to see some straggly/wirey/differently textured regrowth, which looks consistent with how hair grows back after being plucked out. Lastly, nearly everyone with trich developed it at around your son's age.
Has your son admitted to pulling his hair out? In your post, you said "my son doesn’t think he pulls his hair to that extent" - which implies that he might have admitted to doing it a bit, at least? If that's the case, then it's pretty safe to say that trich is the issue. here. He will definitely be under-egging how much he does it, and he will be deeply ashamed of it and won't want to admit it to you, even if you are being super-supportive. (Really, shame is the most damaging aspect of this disorder, rather than the action of hairpulling itself.) And if he knows you have cameras in his bedroom, he will do it in another room.
How are you doing now, have you had the diagnosis confirmed, has he opened up to you at all? What treatment options are you looking at?
Hope you're ok, this can't be easy. It absolutely devastated my mother and she totally blamed herself. Not helped by some ridiculously off-the-mark theories from psych professionals ("it's self-harm! you hate yourself!" / "you're clearly traumatised! did your parents abuse you? are you SURE?" / "no, you're autistic! it's a stim!" / "you have OCD!" / "no, you have an impulse-control disorder!" / "no, you have PTSD!" / etc. etc. ad nauseum). And REALLY not helped by the idiom "I was tearing my hair out" to mean "I was stressed/anxious/etc.". For me, my emotional state has fuck-all to do with it. It's hard to imagine for those who don't have the disorder, but it really doesn't hurt - at all - on the contrary: it feels deeply pleasurable. A bit like popping a spot, but more addictive?!
I still have trich, but I consider myself recovered now because I have fully accepted it (I now shave my head, which is the only thing that stops the urges, and wear wigs). I am also currently under contract to write a book about it, so am au fait with the latest research.
More than happy to chat, to answer any questions you might have, etc. etc., if that would be useful at all. Feel free to DM me.
Keep your chin up x