The reacted excitedly, as dwarves in Tolkien's epic tale were known as miners, and controlled the Mines of Moria for generations. So the Dwarves expect to reuinte with family and friends, expect to feel at home in the mines, and to introduce Bilbo around and spend nights of feasting, drinking and storytelling. They are, of course, disappointed to find the mines all but abandoned.
It is Tolkien's way of foreshadowing the future books in the series and illustrating that Middle Earth has changed, and was changing. That the danger was real and present.