Earlier quoted context omitted.
It's not his definition. Pure means "Not mixed or adulterated with any other substance or material". Here there is JS mixed, hence it isn't pure.
The point. You are missing it. He or she uses CSS for a job for which usually images are used. Hence his or her use of CSS is pure in that sense and it’s also written down that way. It’s not misleading in any way, shape or form. HN. A community of whiny know it alls.
Not that I have any problem with it being pure or not, just with your reply to okal.