I just looked into why that is the case and if you hover over the little dropdown carrot for the "3.8 out of 5" you see this:

Amazon calculates a product’s star ratings using a machine learned model instead of a raw data average. The machine learned model takes into account factors including: the age of a review, helpfulness votes by customers and whether the reviews are from verified purchases.

So a product would just need a small percentage of 5 star reviews in the beginning of the review period.

Oh wow, that is absolutely blatant rating inflation!