But Zhang was teaching as a adjunct (or at least, a non-tenure-track instructor) before he made this breakthrough and skyrocketed (apparently) to full professor

But Zhang was teaching as a adjunct (or at least, a non-tenure-track instructor) before he made this breakthrough and skyrocketed (apparently) to full professor. Adjuncts generally have enormously less time for research than full time professors do (at least if they want to make a borderline living wage).