he's right and wrong at the same time. for example this is my workout split:
back and biceps (muscles you use to pull)
chest shoulders tris (muscles you use to push)
legs and abs (stability muscles)
some people like to isolate muscles more than i do, but if you're doing compound exercises with correct form then there is no need to dedicate one day to just your arms for example. biceps/triceps are some of the smallest muscles in the body and overworking them wont make them grow any faster.
proper training and dieting (IMPORTANT) will get you better results than overworking your muscles then eating junkfood