Nexon didn't get bought out
BlockParty isn't another company that took Nexon over.
BlockParty is Nexon's attempt to "re-brand" itself. It's trying to appeal to a younger audience which it feels will be its target market in the future.
I don't know where you people are coming up with "BlockParty == PunkBuster" as well. That is clearly a bunch of random speculation. Nexon won't switch to PB.