Sounds like temperature problems. Use your nvidia control panel (or ATI equivalent) to set the fan speed to max while you're playing. If that doesn't help, open up your computer and try blasting out some of the dust from the fans. If that doesn't help, buy a new video card that can support whatever game you're playing, since clearly your hardware is working harder than it's capable of doing.
He's actually 100% right. Nvidia cards are famous for temperature issues. Don't believe me? Look up 'Nvidia fire meme' on Google images.
My GTX 750 doesn't overheat and its slightly overclocked.
I think a better question would be : Is the case he's using have good airflow?
Many cases have poor airflow, and with bad cable management, even worse, do I even have to add the word dust?
Also I looked it up, this is one of the things I found :

Yep.