It's not "really" shouldered, there is a lot of space in between the butt and his shoulder which you can see in other videos. As to his accuracy, that target is about 10 yards away - I've been to the range where this video was made a whole bunch. He's also doing this with a 9mm AR, not a .223 or an Ak, which would have significantly more recoil than the 9mm.
Bump firing can be fun, certainly - but there are safety risks. If you're firing an actual rifle caliber, it's not too difficult for that rifle to get away from you in recoil, which then becomes dangerous to bystanders. Bumpfiring is usually banned at most public ranges, and for good reason, mostly because it's inherently unsafe.