Easily accounted for doesn't mean just proving absolute causality - you can account for the issue by either certain statistical tests giving evidence for causat

Easily accounted for doesn't mean just proving absolute causality - you can account for the issue by either certain statistical tests giving evidence for causation, but more easily you write about associations, what gives you evidence for the reduction of confounds (strengthening your evidence, as they did in this paper), and, of course, papers are written to an audience that understands correlation != causation, and are written as such. People pointing out such an obvious thing that is always accounted for in various ways in research shows their ignorance of the specific article as well as the philosophy of science in general. It's just a reflexive response for some people at this point.