[SoLiDUS]

If by IQ test you meant Emode, you would be right to say it isn't foolproof,
as fools have been known to score well on it despite being average.

Culture fair tests exist that determine cognitive abilities with a very good
degree of accuracy, such as the Ravens matrices, TRI (inductive reasoning)
and some at the International high IQ society website: where most tests
requires a lot of basic knowledge, the aformentioned tests require only that
you recognize the underlying logic before proceeding. General cognitive
abilities et al are measured and give a good indicator of future success.
Not at all a guarantee, of course. When he says "smarter than 98% of the
population", he means that his cognitive potential surpasses the majority's.

I'm sorry to rain down on you like this but I'm tired of laypersons bashing
cognitive assessment tests when they know little to nothing about them or
how they work.