https://www.pcgamesn.com/fortnite/playerunknowns-battlegrounds-fortnite-battle-royale-statement
In a nutshell, Bluehole is concerned that Epic Games is copying PUBG. Note that Epic Games is the creator of the Unreal Engine (which they license out to other game companies; Bluehole licenses and pays royalties to Epic Games for Unreal Engine 4 which it uses for PUBG, Devilian Mobile, and TERA console as well as Unreal Engine 3 for TERA PC).
I have an oft-used quote for Bluehole; “pot calling the kettle black”. Bluehole did not create the Battle Royale genre or first person survival mode shooter. Brendan Greene (creative director of Bluehole Ginno) is the modder who created the Battle Royale mod in DayZ (which itself was originally a mod for Arma 2).
Bluehole Studio does not have a clean past. It was originally founded in March 2007 by former NCsoft developers that were working on Lineage III (what was later renamed to Lineage Eternal) who ended up utilizing trade secrets and intellectual property from that game in what ended up becoming TERA (and TERA’s IP ended up being utilized heavily in Devilian after Ginno Games was acquired by Bluehole Studio).
NCsoft did end up filing a civil action and injunction against Bluehole Studio in 2007. While those employees were convicted and held liable for the misappropriation of trade secrets (the courts originally awarded NCsoft $2 million in damages but that was overturned by an appellate court) where they could not utilize any of those misappropriated trade secrets for monetary gain, Bluehole Studio ended up releasing TERA in 2011 in South Korea. TERA itself has been a huge money maker ($100 million per year in worldwide revenues) for Bluehole over the years (so they ended up with huge monetary gains inspite of the injunction).
I call PUBG a windfall for Bluehole because they never really expected the game to end up becoming this popular as it has during Steam Early Access. And now these greedy hypocrites want to protect this without understanding that most everything in PUBG is based on prior art (mods in other games of the exact same survival mode genre).
Bluehole did clarify it isn’t about the game mode but about the fact they license and pay royalties to Epic Games for Unreal Engine 4, and that Epic Games is now making this battle royale style game. IMHO, Epic Games are free to make whatever games they please using the game engine they designed and developed as I doubt either company signed any type of non-compete clause. Sure, they (Epic Games) licenses it out (recouping their costs) which saves other game developers from having to recreate the wheel and designing their own engine (or having to license an alternative one like Unity if Unreal Engine had not been an option).
Bluehole would have a case if Epic Games were ripping off actual trade secrets or ripping off actual assets. This will end up backfiring on Bluehole in a big way if they decide to pursue actual legal action against Epic Games. Actually, a reality check, swift kick to the groin, and a gigantic cup of KARMA would not be a bad thing for Bluehole.