Yield volatility

This is about the concept checker question 11 of term structure and volatility of interest rate on page 156 of book 4. it gives bond stdev and it turns out that yield vol is yield * bond stdev. Why is this the case?

The given std. deviation is in % of mean value. So, the actual std. deviation measured in terms of the mean units is 7.19 x 0.113 = 0.8125%