What exacly is salad fingers about?

[Courtney M]

I watched salad fingers on youtube and looked at the comments and some people said that salad fingers is based on life after a nuclear war and how salad fingers survived and had no one to talk to so started turning into a scitzophaniac (sorry, can't spell it) And how he started talking to himself and his little puppet things. And then i typed in david firth in google and read his description which said " Much of his work is humorous, highly abstract and mostly deals with mental illness, nightmare imagery and surrealism" quote. I just want to know what does it mean when it said "deals with mental illness" Does it mean that the artist of salad fingers (david firth) made salad fingers because HE had those diseases or that he wants to show life through those peoples eyes. And I don't know weither to find it funny or not.