Sand Land takes place in the Demon World.Lucifer looks like a generic devil, but he's actually the true ruler of their universe, Dabra. Only his son, Beelzebub, knows it. In fact, Beelzebub and Goku start their adventures at the same time. We just don't find out what happened to Beelzebub, but we do find out what happens to Goku.
Sand Land is the sixth universe's Earth.Vados tells Champa that on their Earth, some disaster happened, leading humanity to extintion. Sand Land is set in a post-apocalyptic scenario, undoubtely. Beelzebub's father strongly resembles Dabra, and for years many fans thought they were the same character. However, after the inter-dimensional tournament arc in Super, we can easily assume that King Lucifer/Satan is simply Dabra's doppelganger, like Frost is for Frieza. As for the not-so-extincted humanity, well, in that moment all that Champa cared for was Earth's food, which is not so a delicacy when a cataclysm almost erase the civilization. Instead of explaining the matter in its entirety, Vados preferred to put it simple and quick, even if not accurate, since the details weren't interesting in that context.