This shows what I know...
I was under the impression that "pies" referred only to Paiste cymbals, because the spelling looks like it should be pronounced pasty, and the nickname "pies" reinforced the correct pronunciation. But hey, I'm a guy that spent several years thinking that young people were saying "my bag" when they would make a mistake. It made sense metaphorically...like they were taking ownership of the mistake and putting it into their bag of mistakes.
I have since been corrected...my bag.