Amazon calculates a product's star ratings based on a machine learned model instead of a raw data average. The model takes into account factors including the age of a rating, whether the ratings are from verified purchasers and factors that establish reviewer trustworthiness.
The picture give impression of a 3D sticker but it is actually a flat sticker, cut out on a thick sheet. The picture of emoji is just printed over this sheet and does not have bulged spherical surface as happens in many magnetic fridge-stickers. The magnetic quality is good though.