There are primarily two means to measure risk for a stock or a portfolio: absolute and relative measurement. The overall risk is referring to absolute risk, which is measured by standard deviation. Higher overall risk <==> higher volatility <==> higher standard deviation, and vice versa.
Frequently, risks are measured agains the whole market, by beta. Larger beta implies higher market/systematic risk. However, higher standard deviation is not equivalent to higher beta. Some stocks have large volatility, but small beta. Google is an example, because it often moves against the market. Look closely at the x-axises of CML and SML graphs.
As to the errors in Schweser Notes, I just found that they publish errors detected and reported on their website, sorted by books: