This is a reference to a previous Moe's Secret Friends strip, where I hinted that, since the mermaid Moe was visiting was not Maren, he might be secret friends with the whole oceans.
Also, the lack of belly button is explained in a previous post, and the division line was drawn the same way it was here.
I thought of the grudge between merpeople and humans a while ago, and realized later on that this idea kind of explains why mermaids are so often seen trying to lure people to their deaths.