none of this applies to a double-blind, placebo-controlled, randomized clinical trial (which is what this article is).
the reason it's the gold standard for medicine is because the only thing that is different in aggregate between the groups is the intervention. Therefore, it is the strongest possible evidence of causality we have, and does say something about causality (rather than correlation).
It's important to replicate, but the points made by Pearl are not relevant here and the mechanism is moot when you have a causal link shown by RCT.
To be honest, I think a randomised clinical trial is more of a starting point than an endpoint in terms of 'knowing' that an effect is genuine. The 'gold standard' moniker overdoes the authority of the RCT a
the reason it's the gold standard for medicine is because the only thing that is different in aggregate between the groups is the intervention. Therefore, it is the strongest possible evidence of causality we have, and does say something about causality (rather than correlation).
It's important to replicate, but the points made by Pearl are not relevant here and the mechanism is moot when you have a causal link shown by RCT.