Hate to burst your bubble but most people on this site are "PC master race " users.
The person you saw either used used a gen of ease or has a hacked weapon. If it's a hacked weapon. Go on google and figure out how to do it yourself
HAHA and PC player don't cheat either? lololololololol
To the OP - google d3 save editor.
If there is a game, competition or sport. People cheat. Easy as that. Cheating on pc version of diablo 3 is not remotely close to console cheats with hacked weapons. lvl 1 weapon with millions of dmg. Won't find that shit on pc. You have botters and turbohud users, but so many cheat things have been removed from turbohud now that it hardly qualifies as a cheat, more like a illegal UI mod.