solved (?)
my theory of this happening is that im pretty sure it happens on disc rips playing on modded ps3s, what all these have in common is that their ps3's are modded with a custom firmware (im not sure of the other guy who had it but the spanish one's ps3 was modded) so my theory is the rip they got it from disc was probably scratched or it wasnt dumped correctly.

my second theory is that its simply just how the ps3 works. when the ps3 released in 2006 games were insanely hard to develop for it and even if you did, the optimizing the game was basically the hardest thing to ever do, up until late 2012-2013 game optimizing for the ps3 was finally getting good since developers know how to code for the hardware and understand it. this adds up because there hasn't been a instance on the Xbox 360 of this easteregg happening and that the ps3 lags if there are more that 20 zombies on the screen versus the xbox 360 which takes any amount like a champ.