Update:
Maybe that's an useless information but i'm going to post it anyways in case anyone need it.
The shock looks like both air suspension and coil , but in fact is just a coil shock with a sort of protection (maybe againsts mud and water). I Assembled the bike from zero and i had to admit that protection was worth since is the first time i found a still working cheap-coil shock for those types of bikes.
Even the fork had to be disassebled and cleared vut this shock was still fresh.