When build tools run an uglifier on your code this is what the variables comes out as. Takes all your logically named variables and shortens them like a-z. They can make it "beautified" by un-minifying (not all on 1 line) but you can't get their original variables name without the original source.
I think they may have been referring to the names right down at the bottom - a minifier wouldn't use "NWvQtGjjfQX" without having used all the two, three four or five letter variable names.
