I have no idea of the real answer to your question, but, when early releases of Windows 8 were available, Microsoft themselves, boasted at great lengh on the future "Store". It was stated that all applications would be vetted before being plced in the store, in order to maintain a standard.
My own observation, in the latter stages of Windows 8 development is that 1. The Store has now become so large, that it is quicker to "google" for anything that you seek, rather then plough through it. ". There does not appear to beany standard at all being applied. Merely in order to comment and criticise, I have installed and uninstalled many apps across the board, to examine what is available. Many of these are written by codeing amateurs, who have use the well advertised, and comaparitively simple, method, of turning a small application, or simple game, into a full blown Metro. The result is a prolification of , in 60% of what is available, total garbage. No standard is being applied. The available stars, to which you refer, do not, in many cases, relate to the quality of the program.
So, as in my first sentence, I am not aware of any "formula" being applied. I seriously doubt that any group in Microsoft is dedicated to going through every offering and assessing each.
Not sure about the answer to your question. I can only assume that perhaps it involves that actual rating feature within the application settings with respect to "Rating".
But with respect to your particular application I would suggest that perhaps you perform a google image search with respect to Catfish and Quail. I have a four year old grand daughter for whom I install every type of children's learning game available and having an image of a saltwater ray being identified as a "Catfish" and what I presume is some type of Waterfowl being identified as "Quail" maybe a bit confusing and difficult to understand.
Having seen quite a few of these now, I would say you are doing ok.
Other than the two obvious mistakes I have pointed out above, I would give you positive points for actually using quality images rather than cartoon drawing representations of the animals that are present in most similar games.
Having no actual idea, what your design intent was I really can't critique with any specificity. I can only compare it to others that are similar. I like the fact as I've said that you have chosen to use quality images and aside from that I might suggest that you add a brief audio track where possible (on image click) so that the "Lion" roars and the "Kittens" meow, etc., seems to entertain small children and perhaps a "Restart" or "Begin Again" button to accompany the forward and back buttons.