Well, the thing is, Mamanbou looks like a more detailed version of Luvdisc. Obviously, Pokemon don't have to bear exact resemblance to be related. Take Rhyhorn and Rhydon, for example. Rhyhorn is a (somewhat) simple Pokemon, who gains details as he evolves and grows in size, becoming Rhydon. Same case would be with Luvdisc and Mamanbou.