There is no stopping all the hopefulness and delusions of many in this forum.
Time and time again in many threads about predicting future albums, some of the forum members actually hope or predict two albums released in such short intervals.
Nothing in U2's history has indicated they can do that. And they are much older now and nowhere near hungry spring chickens.
As for Mullen's declaration, it does not make sense to call an album 9 months before its "supposed" release, unless it is already 100% complete now and they are just waiting for the proper timing to release it. That is not the case with album release however. Artists try to put it to production fresh from the studio so that the lyrics and music are still current and relevant to the music landscape.
The most likely indications are that Mullen has seen progress in the studio and feels their pace will take them through September. He is getting old and mindless of the fact that he is not U2 alone. There are 3 other members who represent unpredictable variables in the recording process given their advanced ages and busy schedules.
The recording of a U2 album is painfully slow, but the last few tracks are just like the last two minutes of a basketball game - the time says it is close but the actual time it takes to finish is actually so long.
Again, it is 2014.