He didn’t present a theory.
http://dictionary.reference.com/browse/theory
“a coherent group of general propositions used as principles of explanation for a class of phenomena”
“a proposed explanation whose status is still conjectural, in contrast to well-established propositions that are regarded as reporting matters of actual fact.”
In his latest book, The Grand Design, an extract of which is published in Eureka magazine in The Times, Hawking said: “Because there is a law such as gravity, the Universe can and will create itself from nothing. Spontaneous creation is the reason there is something rather than nothing, why the Universe exists, why we exist.”
“It is not necessary to invoke God to light the blue touch paper and set the Universe going.”
PS I called it the atheist story of creation. It is his story (did not use the word theory).