I'm always so surprised when I read such statements from extraordinary people. Why the hell would Shannon of all people have such a distorted view of himself? Is this just hypocrisy, a kind of fake humility, or do most geniuses think they are average?
On somewhat of a tangent, in many ways science and creativity are fundamentally opposed. Science requires constant, humble resignation to reality. And, though creativity may work within the confines of reality, I'd say it tends to have a more rebellious attitude. Shannon doesn't explicitly say it, but he's definitely getting at the fact that the greatest intellectuals manage to excel at both somehow and I think his suggestions at problems solving are an attempt to give a potential equation for doing so.
All that aside I think your question has more to do with Shannon's personality than his intellectual achievements and I'm sure his personality type can be found evenly distributed across the population's IQ range.
If you know a lot about some field, you become extremely aware both of all the things that you don't know that you wish you knew about that field.
If you're really smart you probably affiliate with a lot of other people who are really smart. You also have a sense of how much these smart folks know that you can barely fathom.
It's not an ironclad relationship, of course, but an awful lot of the smartest people I know are humbler than an awful lot of the idiots that I know, and that's my current working hypothesis as to why.
Shannon places Isaac Newton & Alan Turing above the curve, so it a very high bar.
This is Shannon writing at age 36, still at Bell labs producing practical work for the military, often classified and mostly on crypto.
His seminal memorandum 'A practical Theory of Communication' had begun circulating only 4 years earlier and it's full impact was not yet apparent.
What would be the correct view then? To be saying, "I am a genius"? But who says that and is ever a genius?
I think the point is, there is no such thing. Genius is a reputation, and an overblown one at that, but justified by context, such as being the best out of a group of people.
What we should be more concerned about is how ordinary people go on to achieve extraordinary feats.
We're all human with given the same amount of time in a day. Saying some are genius and are exceptions to normalcy is a cop out. Like the rumor that Bill Gates and Elon Musk both have photographic memories. Turns out, there is no such thing as a photographic memory. There are techniques to memorization, but they don't seem to be doing those either. It's shocking I know, but they're normal people.