That it was just a content consumption device, not a creation tool like a "real" computer. He was correct on that account -- the first iPad was mostly a consumption device, but he clearly misjudged the demand for such a device and now Microsoft has to play "catch up" with Windows 8.
Microsoft's problem now is that so many consumers are "invested" in App Store content. Worse -- since consumers are familiar with, and enjoy, iOS its more cost effective for businesses to adopt iOS devices than Microsoft dependent devices b/c training will be easier.
My opinion: I believe Bill is just trying to find fault with the device in this interview. He himself admits he is biased. But what he is saying is that the iPad doesn't have pen input (hand writing recognition) and or voice-input, both of which he believes in integral for a tablet-like device.
They always take a small quote out of a paragraph and make a big deal about it. I saw an old interview before the iPad ever came out with Bill Gates and Steve Jobs talking about how tablets would take over.
Bill and Steve are just people. Their roll in the companies during the later years was vastly different then when they first started. I am sure I will get flamed here, but CEO's are really just puppets and political figures in large companies. Its the engineers and other people that created the projects we love today. Steven and Bill just got the ball rolling.
In short, who cares what Bill says, he spends his time flying around and working on his charities now.