It's the distance from the earth to the moon, obviously. Why would it be anything else? Why would you care about the distance from anything else to the moon?

And yes, it's a big ad hoc bag of hopefully-useful values. It turns out that a big ad hoc bag of hopefully-useful values is, in fact, sometimes useful.

(Of course there's more to Frink than its big bag of handy predefined values. But I take it it's only the big bag of handy predefined values you're criticizing, and indeed that is one of the more interesting features of Frink.)