The monuments are very abstract and have features that could be ascribed to several South- and Middle-American races, as well as that of early Mongolians and several other Asiatic tribes. Language parity is common thanks to a limited set of phonemes and morphemes achievable by the human palate, and ol' Ivan wossname (educated in South America, taught Swahili by his expatriated parents, and apparently trained to hate the West at an early age) gets pretty damn creative in his linguistic analysis.
I've spent the last 30 minutes Google Fu'ing this subject and all of the praise for the book seems to come from the fringe anti-Colonialist set that plagued middle-grade University liberal arts departments from 1970-1990. There seems to be VERY little anthropological credence granted this theory from anthropological scholars outside of a very narrow set, although it's clear the Nation of Islam folks have lept on it.