Josh Marshall says Rove is bluffing:
It's the bandwagon effect. Psyche out the other side. Act like you're winning and you'll charge up your activists/voters and demoralize the folks on the other side. Mainly, get the press to believe your hype and they'll do the charging up and demoralizing for you...
For the Republicans, the difference between a bad night on election night and a catastrophe could well turn on whether or not the party's ground troops really believe all the polls they're seeing. If they do, the demoralization will likely be crippling. And a bunch of them won't even show up. Rove has to create the impression that he knows something the polls don't to keep the Republican GOTV operation from breaking down entirely.
It's that simple.