I believe they use a burnishing tool and "scrape" the pattern into the metal. Tiny bit of metal is displaced making a good place for oil to hold onto.I have seen it used on machine tool ways also.
The scraper is usually a long flat rod with one end hardened and ground to form a slightly curved surface with perpendicular edges. The butt end of the tool is rested upon the top of the operator's shoulder and the operating end is pressed down onto/into the steel's surface at a long angle while also being drawn toward the operator. The operator's hands provide pressure and guidance for the operating end while the backward movement of the operator's body draws the tool's end toward him, across the steel surface. RDH45 is correct about the treatment of the machine tool ways, AAMOF the process of 'scraping' the ways is SOP when refurbishing worn machine tools. The scraping is VERY functional (actually quite necessary) on the machine tool ways but is largely cosmetic when used on rifle bolts.
Scraping is typical of the better prewar rifles while engine-turning largely displaced it on postwar rifles, at least that's my impression.
Regards, Joe
