Tell you what, that guy, whoever he is, ain't lapping none of my stones ! I'll say no more about that.

I think that demonstration beginning at the 9 minute + mark explains the 2mm movement portion of Iwasaki's text. So while he is moving fore and aft with the one motion, he is also moving sideways. A picture really is worth a thousand words, particularly a moving picture. Many thanks to Randy for bringing the corrected translation, and Oz for the video.