You are right to be skeptical. Charles Murray is not the most reputable of scientists, and his book The Bell Curve is full of bad science to say the least, used to advocate for conservative (if not racist) policies.
A fairly quick summary is available on the Wikipadia page for this book (https://en.wikipedia.org/wiki/The_Bell_Curve#Reception) where you can dive deeper by looking into the reference (I particularly recommend S.J. Gould which addresses scientific racism in length in the book Mismeasure of Man). There is also a long video essay by Shaun (https://www.youtube.com/watch?v=UBc7qBS1Ujo) —if you have 3 hours to spare—which does an excellent job of summarizing the bad science and political agenda of The Bell Curve.
A fairly quick summary is available on the Wikipadia page for this book (https://en.wikipedia.org/wiki/The_Bell_Curve#Reception) where you can dive deeper by looking into the reference (I particularly recommend S.J. Gould which addresses scientific racism in length in the book Mismeasure of Man). There is also a long video essay by Shaun (https://www.youtube.com/watch?v=UBc7qBS1Ujo) —if you have 3 hours to spare—which does an excellent job of summarizing the bad science and political agenda of The Bell Curve.