In May 2008 the Obama campaign made a stop in Oregon late in the day. The campaign had, at that point, visited 46 states. Of the 48 contiguous states, they had visited all but two. Oregon brought that up to all but one. He made an off-the-cuff remark, in which he delivered the above quote. But the pause indicated by that ellipsis was quite long. He says "fifty" (clearly, thinking that there are fifty states), then subtracts three for Alaska, Hawaii, and whichever other of the lower 48 the campaign hadn't made any stops in yet, and then says the "... seven states, I think, one left to go," part.
Now, it is funny, because on the face of it it looks like a Harvard-educated guy, runnning for President ferchrissakes, doesn't even know how many states there are. If George Bush flubbed something that badly (as he often did), I would certainly make fun of him. And you're free to make fun of Obama for the flub.
But I wouldn't pretend it meant he really didn't know how many states there are.