From personal experience in my youth, I can definitely say that psychedelics (mushrooms in particular) can help you think in different ways that make your problems seem trivial and imminently solvable. Those changed patterns of thought seem like a revelation at the time -- like the clouds opened and an answer came down from the sky. So I'm not at all surprised with this. That said, this study had only 12 participants…
Surely we've been trying to treat people with severe, long term depression by other means and not had success. This surely wasn't the first treatment that these people tried in trying to treat their long-term misery. How are both of those things taken together not as good as a control group that allows you to draw meaningful conclusions. It really sounds to me (although it would be better to see the quantification in the source docs) that this is a strong enough result to rule out noise.
If your results are strong enough, you don't need a control. If all 12 participants died while undertaking the trial would we say that it needs to be re-run with a control to be meaningful?
The results look strong. Go for pre-registered replication right away. Sod the control group. Everyone with severe long term depression outside the study is already suffering enough to be the control.