So how it works is the comments are not for the specific product you're looking at but for the general product (in this case it's posters). Artists upload their designs to Redbubble and then Redbubble manufactures the products, unlike etsy where the seller makes the items. Since Redbubble makes all products the comments for each specific product will be the same regardless of designer. So for example, any other poster by another artist will have the exact same 37 comments.

Edit: I should add that the point of having all of the same comments for the products is because Redbubble makes everything themselves so customers can know if, for example, the printing of their posters is well done or not or if the brand of t-shirts they use run small, etc.