Yes, it’s right, he says " The key parameter is the fraction of all mutations that are harmful since this is what contributes to the “load” that the population must tolerate. It’s actually very difficult to obtain accurate values for this fraction, but most population geneticists think that a value of one-tenth (10 percent) is likely to be a good estimate. This value is based largely on the number of deleterious mutations in protein-coding regions, but it’s reasonable to assume that it applies to all functional regions of the genome, including regulatory sequences, centromeres, and the like.
This number means that only 10 percent of all mutations in functional DNA regions (e.g., genes) are deleterious and that the other 90 percent are effectively neutral, although there are a small number of beneficial mutations occurring from time to time. If the entire genome is functional and there are 100 mutations in every newborn baby, then 10 of these mutations will be harmful, and nobody thinks that our species could tolerate such a high genetic load."