I wonder how garmin calclate the average rating of reviews

As I just published a new watchface on the store, I always find a guy , who rate me 1 of 5 without any text ,and soon he delete it .

and my average rating is down to 4.7

this guy on the pic

here is my watchface Man of Steel | Garmin Connect IQ

I don't know why ,but garmin did calculate it in average rating.

because the other reviews is all 5 star.