In "Water Margin", what does "his family sells steamed river leaks, which are hot, mild, spicy and crispy" mean?

This is a joke, which is the so-called oxymoron in Western rhetoric (arranging two words with completely opposite meanings and putting them together to create an abrupt but complementary disturbing effect), which seems to be a new Antiques are novel antiques. For example, He Liuzi (a kind of dim sum) has been steamed, so there is no need to steam it; Da Lasu (another kind of dim sum) cannot have the qualities of hot and mild at the same time. Based on this, it can be concluded that it is a gossip of Wang Po, used to tease Ximen Qing, and at the same time, it also indirectly depicts Pan Jinlian's abrupt dual character of positive and negative in "Water Margin"