Its when you add vocal or aural effects to the sound of the sax, for example, the use of flutter tongue or the growl, to "dirty up" the sound. Rock, Rock and Roll and the Blues are where I feel a dirty sound comes into its own. Rasping, screaming solos and note bending all help to dirty up your environment! Pure filth. Bring it on!
A good example for me, would be Bobby Keys playing on Brown Sugar by The Rolling Stones. In my opinion, Keys uses a combination of both of these effects to very good use. He manages to use the flutter tongue and the growl at the same time as well as bending some of the sustained notes hat he plays.
Well, I suppose it would have depended on the circumstance. If it was a mellow piece that warranted a smooth, soft and "pure" sound, then yes it may well have been. If however if it was a piece that required you to sell your soul to the devil, then it was probably a well deserved compliment!
Is it something you still do?
I wonder then, if your lacking in diaphragmatic support when you play? Some times as your embouchure develops you can over blow when you start a note. This could even be a reed choice problem, if your reeds are too hard for instance.