Moving from 4th of July to May 30th does not indicate confidence.
Since they have moved Maleficent up from July 2nd 2014 to May 30th 2014, probably means that they plan on being ready to release Maleficent in theaters by then. Or, That they think they will be ready to be release it by then, because they have finished filming the movie and the reshoot of Maleficent's opening scene or opening scenes will be done by then. So it has nothing what so ever to do with their confidence in the movie. If they weren't confident in releasing the movie or weren't ready to release it, they would have moved the movie release date back further to back in July again or later in 2014.