CTE alone can cause hallucinations and delusions if it is bad enough; drugs wouldn't be necessary. It is possible that it is a combination of drugs and CTE.
Both methamphetamine and cocaine increase the release of dopamine and other neurotransmitters, which, when chronically elevated, lead to oxidative stress and excitotoxicity. This process can further damage vulnerable brain regions already compromised by CTE, such as the hippocampus and prefrontal cortex.
Also, chronic use of these drugs has been associated with impairments in memory, attention, and executive function. For someone with pre‐existing cognitive impairments (from CTE or other injuries), the additional drug-induced deficits can tip the balance from mild impairment into more severe dysfunction.
People associate paranoia with drugs because that is the experience most have when seeing someone expressing paranoia, but that is far from a safe assumption because a lot of mental health or cognitive syndromes also involve that kind of paranoia.
Something like schizophrenia is unlikely given BJ's age (usually happens in late teens/early 20s), and the fact that he certainly has cognitive damage, and that is far more likely to be what is affecting him.
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