I have read in a few places that Arteta is not Guardiola's assistant at all. He has a number of "assistant coaches", and one in particular that is his right hand man, but the title doesn't mean what it does at Arsenal or at most clubs in England. Reportedly, Arteta's role is first and foremost that of a video analyst. He improves the games of City players by spotting things for them to work on and finds tactical weakness in upcoming opponents.
That's not to say, if true, he isn't important and that he couldn't immediately be a good coach, but 1) he is categorically not Guardiola's assistant in the way that Steve McLaren was to Ferguson or Pat Rice and Steve Bould were to Wenger and 2) Guardiola's words about Arteta and his influence have to be taken with a large pinch of salt because old Pep has a long history of hyperbole.