Popular is not what you say it is. We don't know what any of these mean and popular isn't downloads or earnings or anything I can understand. IS used to be sales over time so a new file that got one download would shoot to the top, and then slowely drop down in the search.
Like Sue says, new isn't always new. Relevant is supposed to be best match, not new or popular, but I doubt that.
Sorry but every agency has their own idea of what's popular, best match or relevant, you have to try to guess what they do and some like SS are impossible and illogical.