Black holes don't emit x-rays themselves, matter falling into black holes heats up and emits x-rays before it is swallowed up. The Hawking radiation is different (but not at all ad hoc, as the article said); it's actually emitted by the black hole itself, and much weaker than the x-rays. Also, black holes are not usually "defined" to be singularities, it’s just that every current theory we have inevitably leads to singularities. String theory is different because the fundamental objects, strings, are extended (they have length), as opposed to points. It's been known for awhile that this would prevent singularities because the strings are spread out. What has come out more recently is the idea that the strings could stretch from the center of the black hole out to the edges, and somehow encode the information there (again, note that the key is that the strings have a length). This way information is not lost, which is VITAL to quantum mechanics.