FYI, Mine looked like that once, and I made them all nice and shiny with a dremel tool and a soft wire brush attachment. -Didn't matter, as the corrosion was also throughout the length of the battery cable for several feet, not visible until doing an autopsy by slitting the cable insulation and peeling it off the cable.
So all may be well for now, and your friend will certainly have good battery to battery connector contact, but if he has trouble down the road, take a serious look at replacing that cable. Had this exact same problem on all five Pontiac'* I've owned.
97 SE, teflon wiper blades, Dunlop Sport A-2 tires, Leather steering wheel cover, Pioneer DEH-P480MP mp3 CDRW head unit, Pioneer 12-disc changer, iPod hookup, Boston Acoustic 3 way 6x9'*, Boston acoustic separates in door pods, Alpine 4 channel amp in trunk. Magnaflow dual outlet muffler and Ractive stainless tips. Autozone rice pipe and K&N 4750 intake kit. Clear corner lights. Energy Suspension end links.