Slightly skeptical. The turbocharger is pretty much irrelevant at idle speeds and the only way an O-ring would cause an idle problem would be if it allowed an air leak that was below the throttle plate, not in the intake tract between the throttle plate and turbocharger.
Any kind of minor air leak above the throttle plate should not affect the idle but could possibly cause a hesitation or bucking problem.
It would be interesting to know which O-ring he’s talking about and where it’s located.