Tip: Some stores, realiizing you can return a product and re-buy it at the current discounted price, will retroactively price match themselves within the return window.

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.

People don't want discounts for one person while another gets overcharged.

Yeah, maybe you have more faith in humanity than me, but I think there are tons of people who would be ok with this assuming that they're the ones getting the discount.