I think you're right, and I now feel I misinterpreted his comment.

And what the pharmacologists are trying to figure out is why you’re both having this ostensibly life-changing experience with the shrooms

On that though, my point was that the "feeling more positive" / helping against depression aspect is in my mind purely the result of the experience itself - that is, the actual events you experience while under the effect and your own self-reflection and integration on them - and not a "direct" pharmacological consequence of the compound being administered. Software (consciousness), not hardware (chemical reactions in the brain on a lower scale) - yes, I know the analogy sucks but I'm not sure I'm expressing myself properly. As such, I don't see how pharmacologists could figure out such a thing given our current abysmal understanding of consciousness itself - perhaps psychologists could venture a guess, but that's about it.