As Rat describes Toad and his hobbies, his annoyance is clear. In order to afford hobbies like this, Toad must be quite wealthy—perhaps even wealthier than his friends. Toad’s terrible rowing, however, suggests that he’s doing a poor job of looking the part of a wealthy gentleman. The note about “animal etiquette” suggests that manners are a huge concern on the riverbank. This reflects the context that the novel was written in (Edwardian-era England), where propriety and gentlemanly behavior were extremely important. For the animals, it’s important to use goods manners so that social situations can proceed smoothly, which is why Mole doesn’t say anything about Otter’s disappearance.