Saw the TV episode and heard post mortem episode. Unlike previous 'celeb guests' Bridget Christie asked some v useful questions and towards the end I thought she was gently suggesting that his own mental state was possibly a key source of this. E.g. he moved the chair and brought the photos down himself but couldn't remember it.
Julian and Danny / Evelyn kept coming back to saying lots of people saw or heard the same thing but it's so subjective - young lads all joining in with seeing the slenderman thing, his mate hearing things - basically light / shadows and a breathing noise - they're things you can persuade yourself are sinister in a heightened atmosphere and egg one another on with and half believe it. Especially when there's a story to tie it together.
I do think Julian was much more traumatised than anyone else, he was awfully young to have lost his Dad so suddenly and then watch his Mum dying and having to go back to that house on his own. His mate seemed to have been pretty worried about him - thought he was having a breakdown - and I note the mate said he was still a sceptic. I think he could have said more but was being protective. Julian said his friends would be cruel to keep on pretending to have seen things but I don't suppose it's that simple - they might not have known what they saw / heard and it'd be hard to backtrack anyway.
Poor Keiran has to keep reaching for dafter things - ergot, rare hearing condition etc - because once you've eliminated 'making stuff up for a laugh' and I don't know how they do that, the overwhelmingly likely explanation for all their 'cases' is people scare themselves, it's contagious, look for faces etc where there aren't any, have poor recall of events, timings and things seen, and are often mistaken, exaggerating or misremembering. But then retrofit these things into stories. I guess Keiran can't just keep saying this.
In this case, trauma and mental disturbance played a part I think. I'm Team Sceptic of course.