It’s a flattering phrase, not a thoughtful one. It gives the illusion of higher level thinking that’s beyond our actual ability. The phrase also justifies writing without thinking, i.e. most internet comments.
The best thinkers I know mostly use writing for refinement, distillation— as a tool. The worst thinkers I know are owned by writing; they require its fixation & stimulation upfront to compensate for limited attention spans.
This way of phrasing it is needlessly confusing. Writing is a kind of thinking--one of many--but it's not equivalent to thinking.
Dialectical thinking, for example, produces similar results.