With that degree of seriousness it can be not HPPD but underlying psychosis or schizophrenia that has been activated by the drug. It happens with cannabis too. I hope they are followed by a psychiatrist and on proper medication.
I agree with you. I believe psychedelics open a door in in the brain that can never close back. A lot of people have psychiatric fragilities and have no business trying these substances. Hppd occurence is closely related to past psychiatric symptoms like anxiety or depression.
One heavy dose of mushrooms significantly & permanently altered my visual perception: I see colors a lot brighter, a lot more saturated, and with tones & hues I wasn't really perceiving before. It's not technically an hallucination I don't think it's hppd, but it's something.