CPU was a more common term in the earlier days of home computers, when peripherals other than the motherboard were usually housed in their own separate cases.
It can still be used metaphorically to refer to a computer. However, names like: Computer, PC, or Rig, are a better choice so as not to confuse anyone nowadays.
The only people I've heard call their PC a "CPU" were extreme computer illiterates who owned some Compaq Presario "multimedia" computer and used it to e-mail granny.

That's because the dude's a retard. He has no clue what he's talking about. " The CPU plays a huge role in rendering graphics" No it doesn't. The only time the CPU is effected in graphic rendering cycles is when the CPU can't keep up. But that's not exactly a huge role. that's what intelligent IT users call a "bottleneck."
The kid hasn't a bloody clue and needs to start googling before he makes himself look even more like a jackass.