I think Apple meant something very specific as any other reading doesn't make sense. They are saying it is "above dispute". Apple knows what they licensed.
No one is questioning the existence of the patent - it's the validity of the patent that's being doubted. Given the current processes followed by the USPTO, existence says _nothing_ for its validity.
It would be but for the distinction between "undisputedly" and "undisputably". All this says is that it hasn't been disputed, not that it can't be.