That xkcd comic highlights the problem with observational (as opposed to controlled) studies. TFA is about A/B testing, i.e. controlled studies. It’s the fact that you (the investigator) is controlling the treatment assignment that allows you to draw causal conclusions. What you happen to believe about the mechanism of action doesn’t matter, at least as far as the outcome of this particular experiment is concerned. Of course, your conjectured mechanism of action is likely to matter for what you decide to investigate next.
Also, frequentism / Bayesianism is orthogonal to causal / correlational interpretations.
I think what kevinwang is getting at, is that if you A/B test with a static version A and enough versions of B, at some point you will get statistically significant results if you repeat it often enough.
Having a control doesn't mean you can't fall victim to this.
AB tests are still vulnerable to p-hacking-esque things (though usually unintentional). Run enough of them and your p value is gonna come up by chance sometimes.
Observational ones are particularly prone because you can slice and dice the world into near-infinite observation combinations, but people often do that with AB tests too. Shotgun approach, test a bunch of approaches until something works, but if you'd run each of those tests for different significance levels, or for twice as long, or half as long, you could very well see the "working" one fail and a "failing" one work.
Also, frequentism / Bayesianism is orthogonal to causal / correlational interpretations.