Double, they didn't clone buu, they just tried to make one of their own and failed horribly. And they know about Buu because Freeza knows about him. He mentions him directly in Resurrection F as well as Beerus, who Freeza has met.
No offense intended, but... is "failed clone of x" really the only idea anyone can come up with? Oh and, way to just piss on the "no majins" rule by making one who's clone so you can technically say you followed the rules. That's totally not eploitive in any way. <_< Here why don't I just scrap Nero and make a guy who is a failed clone of Vegeta while we're at it? I mean everyone else is doing it.
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Nah, still have to check that out.
@Archmage MC
*points to profile pic* I think that's answer enough.
But yeah, I've heard of Shoddycast. I like their videos, especially their Storyteller series.