I don't think the experience was opiate withdrawal, the effect is similar, I mean all the same symptoms... I think what they experienced is a bad trip from mescaline, which can happen, surprised more people don't mention how bad mescaline can be when it turns on you... I've had one myself from just too much mescaline alone but friends have had them from combining large amounts of methylone with just 200mg of mescaline... it's a horrible horrible experience and I don't wish it upon anyone, your skin crawls, you feel all emotions all at once, time slows to a crawl, and you cant get comfortable in any shape or form, I don't even want to think about it... but I think there are 2 factors involved, one is set and setting which is often underestimated with mescaline, it is not necessarily the same set/setting as other drugs, 1 thing I've learned is that it is a terrible drug to do on your own, for me that precipitates a hyper loneliness feeling... and as others have mentioned it gets potentiated by many other phenys.... when it goes south, it really goes south... but normally very nice, I like to mix with mushrooms for an altered experience, not too dissimilar to AMT.
I will agree with others though that the negative experience can often be a positive one, the bad trip seemed to really make me re-evaluate, it made me question the value of things and also cured a restless leg that I'd had since childhood. I was thankful to have gotten out of it.