“For the fourth time in Doctor Who history, Coal Hill School is coming to the aid of the TARDIS,” Moffat said. “In 1963 teachers Ian Chesterton and Barbara Wright accompanied the First Doctor. These days it’s the turn of Jenna Coleman as Clara Oswald. And very soon now, Sam Anderson as Danny Pink will be entering the world of the Doctor. But how and why? Answers are coming later this year in Peter Capaldi’s first series of Doctor Who!”
You get that? "Peter Capaldi's first series...?" If we didn't know better, we would think that Moffat was trying to defuse a bit of the rumor without giving it the credibility of commenting on it directly.
Actually, since we don't know better, that's more or less exactly what it sounds like.
The original report cited multiple, anonymous inside sources who reportedly claimed Capaldi would only do this for a year before moving on, as he "was selected as a 'single season Doctor' in order to steer the show in a new direction and pave the way for an even more radical (and possibly more controversial) choice for the role."
They speculated that the next Doctor could be female, or that the "new direction" could be Moffat's retirement from the series, but neither of those speculations seem to be based on anything in particular.