He probably also thinks he's a better writer than Bob Houk. He may well be right on the latter point, but on the George Owell/Bob Houk spectrum, he's probably well over on the Bob Houk side.
Self objects to Orwell's passion for simplicity and clarity. Given that the the starting point of writing is (or should be) to communicate, one suspects that Self has yet to master an understanding of his trade. This lack of understanding, unfortunately, seems to be widespread among current writers. He summarizes his own limitations in what appears to be an attempt to mock Orwell.
I like Orwell's writing as much as the next talented mediocrity.A bit of attention to clarity might have saved Self from calling himself a mediocrity.
To be fair, this is probably just an attempt to get people to pay him some attention, and it seems to have succeeded.