Nassim Nicholas Taleb is saying that the second part is likely accurate - e.g. low IQ people are accurately assessed - but the former part is off. This graph: https://cdn-images-1.medium.com/max/1600/0*76fPv686eOXo1b7F.... shows how he claims IQ scores correlate with outcomes, i.e. as you move away upwards from < 70 IQ, its predictive power plummets.

Said simply: stupid is stupid, but we're not totally sure what smart is.