Re: Blues scale: is this accurate?

I have an online friend, a working jazz pianist, who wrote me the
following:

This blues scale is entirely inaccurate because there's really no such
thing as a blues scale. At best, certain cheap book authors have
touted the minor pentatonic as a blues scale, possibly adding the
diminished fifth or augmented fourth. But, actual blues music rarely
uses this combination of notes in a recognizably scalar fa****on.

I really don't understand what he's talking about.  But when I played
through Mark Levine's book, I didn't understand all the chord
analysis, either...