Right but that would also be true and exactly what you'd expect if interviewer mainly judged technical competency on ability to communicate. Since the form is self reported it's impossible to separate out whether the correlation is causal (poor communicators are poor technically) or due to interviewer bias (poor communicators have a harder time convincing interviewers of their technical chops) or even other factors (being flustered hurts both a candidates communication and technical skills).

This is after all an advertorial piece of data spelunking not a study.