The phase diagram of carbon at extreme temperature and pressure is pretty much unknown. We don't even have any really good studies of liquid carbon. So it's entirely possible the core of such a white dwarf would be made of some other phase of carbon. See, for example, this figure of the carbon phase diagram from density functional theory, showing that over a terapascal, diamond is unstable. Stuff is not the same at the core of a star (even a small one) as in your backyard.

It's not that you're wrong, you're just using different metrics. In physics (and astronomy, I think), the authors are usually listed in decreasing order of work done, starting with the person who did the most. The people at the end of the list have done so little work, why are they even on the paper? Because, as you say, they are listed in increasing order of importance (read: amount of grant money received). If you have enough people, sometimes they just throw them all into alphabetical order and pretend that everybody reading the CVs of the people who actually did the work will somehow know that they did.

This guide may also be helpful: PHD's Guide to the Author List

Here's the paper: An estimate of the electron density in filaments of galaxies at z~0.1.

The student got listed as first author, which is cool for her. The paper itself is a follow-up to Pimbblet's (the actual prof with the actual grant) 2004 study of filaments. The major finding seems to be that the press is gullible enough to print anything if you say an undergrad did the work. In this case, the press manages to avoid looking like total idiots, since the study is pretty cool and interesting. Nonetheless, the hype is vastly out of proportion to the significance.

Well, I read all the comments so far and nobody has discussed the actual new parts of the model. The novelty is that the destroyed moon is assumed to be differentiated (The heavy metal and rock fall to the core and the light ices stay on the surface.) and Saturn was in its very early stages, when it was hot and its atmosphere greatly distended. This means that as the moon spirals in toward Saturn, its icy mantle gets stripped off by tidal forces first. That makes a vast disk of icy material from which the inner icy moons and the ring system are formed. Since the denser rocky material at the core of the moon is less affected by tidal forces, it impacts the extended atmosphere of Saturn and gets swallowed up before it has a chance to contribute to the disk. This explains the composition of the rings and moons better than previous models.

The point is not that it was a moon. There was no collision. Takeaway point if tl;dr:

The rings were formed by tidal disruption of a moon with an icy mantle and a rocky core.