There is no reliable answer to this question. Amazon uses several names to market similar services across the country. If (in your market) Prime Now offers general merchandise, and you just happen to order groceries, the merchant account used to bill the transaction will likely not be a Whole Foods account.

There is some useful discussion in this thread: Freedom 2020 Q2 bonus categories: grocery, fitness clubs, gyms & "select" streaming.

Start reading at post 29 and continue to at least post 50, with particular attention to post 38 which is a good summary of the diverse Amazon grocery delivery services.