Not a copyright lawyer, so take this with a grain of salt:
One of the core limitations on copyright is the idea-expression divide. Copyright does not--cannot--protect an idea, only the expression of the idea. (There are other limitations on what expressions themselves can be protected, but if it's not even an expression, you're hosed). Of course, this itself isn't a clear-cut and easy divide, and is endless wishy-washy.
So what allegedly copyrighted material has been lifted here? Well... as you dig into it, it's really a stretch. The argument is that PUBG copyrighted using a military-style helmet in a shooter game. No, seriously, ¶57 is arguing that using a particular "Russian special forces or 'spetsnaz'-style helmet" is a copyrighted element. ¶59 ups the insanity by arguing that using clothing is copyrighted. Not specific kinds of clothing, just regular streetware in general.
Again and again, most of their claims on the aesthetic being copyrighted boil down, essentially, to "we copyrighted using military-style equipment, casual streetware, and a vaguely war-torn, somewhat austere Eastern European-ish environment as the setting for a shooter game." Which is not copyrightable for the even more basic fact that this predates PUBG by a long-shot.
The two strongest copyright claims to me are a) the use of the frying pan and b) "Winner Winner Chicken Dinner". The first claim itself is pretty weak, but it's one of the strongest by simple virtue of its actual rarity in games, so PUBG may have a viable claim to have actually originated it. And the second claim is weak because I'm not sure it's actually infringed--the claimed infringement (¶101) is that the win screen has a cooked chicken on it, not the actual phrase.
So the basic summary I have is that, while Free Fire is definitely a rip-off of PUBG, PUBG's aesthetic itself is so generic that it's not really copyright infringement.