This looks like that summer rewards program they did last year. You got points for buying Kindle books, print books or borrowing Prime books, and then you could redeem points for e-book credits. Maybe they're extending the program to all users, or maybe a bug caused the old points display to reappear.
edit: here's an article with some screenshots showing how the rewards worked
https://booksliced.com/books/amazons...wards-program/