I think it's more that they're smart as hell but know very little or have poorly developed taste. So you have to give them a short leash otherwise they'll hang themselves with it through over-engineering and accidental complexity.
The literal quote from Rob Pike is "They’re not capable of understanding a brilliant language but we want to use them to build good software. So, the language that we give them has to be easy for them to understand and easy to adopt.".
