Thats crazy, I had no idea! I want to do some test swatches with my crochet hooks now. I wonder material effects it this way, if theyre the same mm there should be no difference.
I dont think this is accurate for everyone or every situation. For example, sometimes when one uses a smooth yarn with smooth metal needles, one would hold everything tighter to keep stitches from dropping, and the grip on the yarn will be tighter leading to tighter gauge.
chekccard