So they peeled the banana to save on the weight, because the price is weight based.
They saved 0.29 PLN, assuming that they'd also need to bag and label an unpeeled banana when buying it, that the peel is 35% of the total weight and disregarding the wrongly calculated weight x price on the first line.
My local grocery store sells bananas by quantity instead of weight. Despite a higher sales tax I pay about the same for one banana and I don't have to bag and label it.