I have no experience with HPPD myself, but i wonder if it is real.
It is very real!!!
There's also quite some scientific work about it, but it's still not fully understood.
IMHO it's probably several different effects contributing. E.g. a study has shown, that for some percentage of people HPPD gets significantly less if dopa levels get increased.
I also have HPPD, and it is really like that for me: If I take a strong dopa stim, the HPPD immediately stops, but after the stim effects are over, I get a stronger HPPD for some time (maybe depleted dopa levels?).
I personally think that usually the brain has several "awareness filters", and somehow you can "unlearn"/disable them (on psychedelics, but probably also otherwise).
E.g. the typical tracers of HPPD: That's actually basically how the eye delivers the data (as I saw once in a scientific documentation about research of artificial retinas for people who got blind)! But the brain has learnt to compensate and hide this, so that you're not aware of this sensory limitation of your retina regarding fast contrast changes, and get the picture as reality really looks like.
Also the sensor noise of the eye is not insignificant, but it seems the brain has learnt to hide it from you. But on HPPD you get the unfiltered "visual noise". IMHO simply a filter has been removed.
But these filters are very helpful in your daily life, that's why they are there. And lacking them is mostly an impairment, IMHO.
Again these personal derivations are just my POV. That's what it seems to me, from my personal experience...just a guess...
Lol, I once had the theory, that psychedelics switch many such filters off. And if you then consciously get aware of them, and even find them disabled very fascinating, that the brain then basically concludes you like this version better, and switches off the filter.
So I wouldn't give too much credit on my guesses...