People on drugs don’t usually make the most reliable observers. But I suppose if you can insulate the trippers from one another their answers wouldn’t influence each other. Then you could interview them about the same scene and see if you get different answers. Again, these wouldn’t be reliable observers and idk how eloquent their answers would be under the influence.

All of this to say I’d put my money on drugs causing hallucinations, as we have decades of research which confirm this.