Everybody that is using emacs cares does not imply that everybody that cares is using emacs. It's a common fallacy, and it is one of the few that remain important even on non-boolean logic.
"Emacs -> Cares, therefore Cares -> Emacs" is a form of abductive reasoning. It's only a logical fallacy if you treat it as though logic guaranteed the inference was true. If you treat it as, e.g., input helping to form priors in a Bayesian model, it can be useful information.
Let's say you have 100 programmers. 20 of them "care". Of the 100, 5 use emacs. P(emacs) = 0.05. If all emacs users care, then P(emacs|care) = 0.25. If I wanted to model this phenomenon, I shouldn't ignore the correlation just because it's not perfectly causal.
Or in plain English, if you care then there's a greater chance you'll be using Emacs.
The fallacy if any is assuming likeliness implies implication. This is commonly known as stereotyping, but it's perhaps more clearly described as generalizing a group stereotype to the entire group.
I do really hope nobody is reading that article thinking about prediction. It's completely full of weak proxies that will lose any predictive power as soon as they are used.
(And that's also why you care about causation even if you are only looking for prediction, because you don't want your proxies to change their meaning as soon as you act on them.)
It is indeed full of correlation that can unmask interesting facts if studied further. And the GP complaint is meaningless if viewed from that angle, so I do really think he was talkinga bout causation.
