Here's my theory behind the Salad Fingers:
It's supposed to be set in the the future after a nuclear war when most people have died and he is one of the survivors.
The finger puppets are supposed to be friends he had that died due to the nuclear war. He has obviously gone mad and his skin is all green cause of the radiation and some of the other characters like the armless guy in this episode and the boy in the episode 'cage' are people who have been deformed because of the radiation.
What do you guys think about this crazy cartoon.