This can be stated more generally:

If you didn't explicitly control for it, your results probably only reflect selection bias.

I'd say that it is definitely possible for selection bias to indicate a causal relationship though. Because hiring and compensation isn't just controlled by technical ability or productivity. So there is chance a supposedly non-causal indicator will have a direct impact.

For instance, let's a dev with a really unremarkable resume gets paid significantly less than his coworkers in a really hot subfield because all his coworkers have a top-10 stem degree, research with top professors, and work experience at really hot startups. It's likely if he is a decent negotiator the underpaid dev's compensation will eventually revert to the mean. That will be the compensation of an extremely marketable dev if he can sell himself as a dev with really valuable experience.