They don't misunderstand at all. They don't want them forcing the app down their customers throats so they can collect data on their buying habits and sell it. The unfair pricing is just them forcing people without the app to pay unreasonable prices.

Discounts have a good reason, mostly advertising and some seasonal discounting and lots of storage clearance. So this is fine and to be expected. Nothing unfair about being incentivized to buy seasonal food because its cheaper when its growing in your region at the moment. This is where capitalism gains some efficiency for food distributing. Most stores in Germany announce the discounts up to one week prior, so people can somewhat plan their discounts to save money.