If you want to play this game under 64-bit Linux then you'll need to get hold of the Unity support stuff since it's not included in the zip.
I found the files I needed here:
With a bit of digging in the sub-zips you'll find a Variations folder. Then you should be able to do
cp wherever/Variations/linux64_withgfx_nondevelopment_mono/LinuxPlayer PigEatBall.x86_64
cp -rvf wherever/Variations/linux64_withgfx_nondevelopment_mono/Data/* PigEatBall_Data/