I had a guitar entrance exam yesterday regarding improvisation. The guy put on a A blues backing track and told me to improvise. As I'm not a blues guy myself, I went and improvised on the A major scale (Ionian mode). After a few seconds he stopped me and asked me if I was playing on the pentatonic, I said no and that I'm currently playing on the Ionian mode. He told me that the pentatonic is more appropriate to blues and to play on it. I said ok and proceeded to play on the F# minor pentatonic scale, since its A major's relative minor. He stopped me again and told me to play the A minor pentatonic scale, saying that's what gives it the blues feel- playing the minor scale on a major chord progression (Am pentatonic on A blues chord progression). He failed me at the test (even tho my improv wasn't anything close to bad).
Note: this was not a 'blues improvisation exam', but simply an improvisation exam.
Now my question; was my 'mistake' that serious? Yes, I'm not a blues guy and my improv was not so bluesy probably, but still, failing me felt totally out of the blue.
Edit for clarification, since this came out more as a rant: Is it obvious and known that minor pentatonic should be played on major chord progression (Am pentatonic on top of A) in blues, and are other scales (pentatonic on relative minor/other modes) used as much in blues improvisation.