The bright line distinction is Pepsi watching Food Lion's end-consumer pricing and trying to force it up in order to mollify Walmart.

I actually doubt this is remarkable in the world of major producers and retailers (e.g. I've heard anecdotes of brands sending around reps to ensure that their shelves at retail stores are appropriately well lit and placed, so having an agreement on price seems pretty normal). However, it's probably a good case to get the public thinking about the desireability of such an oligopoly -- evidence that it's not merely better economies of scale and logistics that are keeping Walmart's prices low, but also explicit, private deals that feel shadier. I don't know that anyone did anything objectionable here given the norms and incentives in front of them, but it's a bad look for those norms and incentives.