So there are purpose built mosh pits in Singapore? If then, all concerts that people are expected to mosh should be held there.
You are lucky the body surfers were not arrested because technically body surfing IS illegal in Singapore, just like technically 5 person gathering together anyway can be arrested for illegal gathering. It just depends whether the police wants to arrest you.
So guys, don't push your luck. You choose to mosh and you jolly well know that you are not made of stone. It's your choice. You are responsible for your choice.