So the dopamine theory isn't really good at explaining much...alterations in nmdar signalling explain more but the link between the neurotransmitters and actual symptoms is at this point primarily based on responses to street drugs like pcp or cocaine as they act through distinct pathways and can cause similar effects. Most people who do research don't believe it's that simple with some areas of the brain being over or under stimulated. For example simply losing your vision can cause visual hallucinaitons in something called Charles bonnet syndrome....you're not mentally ill at all you just hallucinate due to sensory deprivation and this can be mimicked in float tanks etc where you aren't getting input you tend to hallucinate. There is no some sort of chemical imbalance just a lack of input. Delusions well I haven't even seen speculation as to what causes that but in my mind it's more important that the meds work to stop them over time and they do.

So back to your question....is it delusional....maybe it sounds more like OCD type thinking but it could also be delusional. So there are a couple of kinds of delusions one is called bizarre one is not. People with schizophrenia and related conditions often have the bizarre ones...ie there is a secret organization of psychic doctors that wants me to join them and this is my initiation. In contrast there is another disorder called delusional disorder...now the definition has changed in the dsm 5 but previously the delusions had to be non-bizarre ie plausible. The cops are after me etc. These delusions are things that are actually possible in this world but a little weird and unlikely and probably not the most rational conclusion. They changed it because the definition of bizarre was so subjective but yes you can have delusions that are pretty realistic. But here is the thing I'm not an md I can't tell you what it is or isn't....this is something that's impacting his life in a negative way get him to a doctor and get it dealt with. Once he's 18 you can't do anything so get it dealt with while you still have the ability to do so. For this I would say see a psychiatrist so meds can be used...if it is a delusion it doesn't matter how much you talk through it....