It can be almost anything, that's the point. For example, much closer to home, we have occasionally found heavenly bodies not quite where we expect. With Mercury that turned out to be new physics (general relativity). With Uranus it turned out to be no new physics but a planet we didn't know about (Neptune). With the Pioneer probe it turned out to be a tiny thrust from radiation from its power supply bouncing off its antenna dish (well known physics that nobody had realised needed to be applied). So that's everything from "oh...duh" to rewriting physics from the ground up.
That's not really what we do here. Unless somebody has a detailed knowledge of neutron star physics their speculation isn't worth a whole lot. And people with detailed knowledge of neutron stars are more likely to publish in journals than here. You could search for papers citing the one on arxiv - that's where there'll be meaningful speculation. The abstracts will give you a clue what they're talking about, even if you don't follow the detail, and that's a topic for discussion.
