Pretty sure he means that while you can draw smaller than 6mm, you won't be able to position it accurately. I've tried using capacitive touchscreens and styluses, and they are not precise at all.

Your fingers don't have that kind of accuracy either. What you do have is precision in your finger/hand/arm system. Moment arm dynamics are far more important in precise drawings than addressable accuracy. The best digital drawing tools I've found make use of stroke dynamics rather than sensor sampling to produce precise and high quality strokes.