This is kinda anecdotal, but if you have ever done shrooms/LSD, you would understand how extremely unlikely this is. I generally should never say "false" with absolutism, since it is plausible, but in this case, given the users previous statements, I would bet significant money that he has no evidence of festival goers doing this with mushrooms.
A good trip is usually around the 3.5 gram mark based on average experiences. If you do this, you are going to be fairly "fucked up" as people say. Its not gonna be a purely positive experience like MDMA, where once the effects wear off, you are going to want to do more to get back to your happy place. Most reality warping trips end up with person wanting it over because its so exhausting.
The next day, if you really want to have the experience again, you have to do something like 5 grams to get the effect. The next day its going to be like 8 grams. Over a week, you are going to be ingesting something like 30 grams - in many places where shrooms are illegal, bringing that much to the festival is likely going to get you involved with security as intent to sell/distribute.
LSD is way easier to do this with, as dosages last longer (12 hours on the average), and multiple tabs or it in liquid form is way easier to sneak in. However, again, the reality warping trips are not exactly pleasurable and quite exhausting, and you still have to do a boatload towards the end of the week, to get the same effect, which costs money and is a waste of a drug (and money).
The way people consume psychedelics at festivals is usually in smaller dosages, where they are certainly not disassociated even remotely Doing this for a week is arguably less harmless than drinking enough beers to get a buzz every day.
Weed/alcohol/mdma are much more common things that get used on a repetitive basis since the effects are pleasurable and you can redose to get back to euphoric state.
There are definitely people that abuse psychs in general, but this is more of a personality issue than a drug issue. People can abuse generally harmless things like video games, and ruin their lives.