Exactly...
we know that Lavos is a giant freakishly huge space monster that comes. smashes into Earth, sucks life out of the planet, damns it eternally, and then reproduces. He also has manipulation over dimensions and time.
But for all we know, he could have damned countless other planets. He could be the first, last, only, or just plain average loser of his kind. He could have had 0 children before Earth or 10000. He could have a day job back on the Lavosian homeworld, and this is what he does on vacation... Ok so maybe not the last one, but technically its possible.