That was a joke. Let me tell you the reason why it is funny...
What did the sea say to the seashore?
What did the sea say to the seashore? Nothing, it just waved.
This joke is a pun. The humor in this joke is that the ocean normally has waves on its surface, so the could be said to constantly be "waving". To wave also means to move one's hand back and forth as a form of greeting, so "waving" could be said to have two meanings.