Tobermory Explained

Everyone in the story is really shallow. The entire piece has a sort of irony, because they make a big deal out of something that's not that important (the cat knowing about their private affairs) and they make light out of something serious (the last line).  The last line means that if he was trying to teach "the poor beast" German irregular verbs (German is considered a harsh language, irregular verbs in any language are a pain in the ass) then he deserved the death that the elephant inflicted on him.