While I don't know if it's actually deserving of the title "implausible nonsense", I think its important to remember that stupid is as stupid does, and same goes for smart. Someone isn't smart because they have the trappings of intelligence, its because they did something smart.

"its because they did something smart" So intelligence == 'achievement'? That makes no sense.

As for nonsense, ok I'll retract that, it is an interesting but highly implausible topic that gets a large amount of discussion relative to it's likelihood. It's actually just another way of phrasing "Does God exist?" If there was a computer (God) simulating this universe and controlling it, then it'd require a host universe for itself to exist, and it's complexity has to be greater than what it is simulating. Therefore it is less likely, and not by an insignificant amount.

I guess its true that you can't just equate intelligence with achievement. In my own life, I think I've increasingly used achievement where I used to use intelligence to gauge how 'smart' someone is. That comment was also trying to get at the annoyingly pervasive belief people seem to have that you must be smart because you are a mathematician, say. As an example, novices might think someone is good at basketball based on how they look on the court- but you wouldn't say someone is good unless they actually had a big positive effect on how often their team won. In general, I guess when I say smart, I mean "good" in some abstract sense.