My recommendation is to read the academic sources, not the guy who simplified materials to an extent that things are lost in the translation leading to misrepresentation and misunderstanding.
Also, always read the negative reviews. Sometime, they are bunk, but they sometime can be very informative.
I've checked the sources from that book and they seem legit, including papers and articles[1]. Besides, the reviews of that book are very positive [2].
[1]: http://guides.skylinecollege.edu/c.php?g=279172&p=1861295 [2]: https://www.amazon.co.uk/Outliers-Story-Success-Malcolm-Glad...