whether the total fund outperformed a pure indexing strategy - 2015 morning q5

why when we trying to see if the fund outperformed a pure indexing strategy we are comparing total fund return to fund return at risk-free asset and asset category level, not benchmark level? Where is this on the book? thanks

Book 6 - Reading 31 - Section 6.4 - Conducting a Macro Attribution Analysis - Asset category (where it says this is a pure index approach, or the policy allocation towards systematic risk, etc).