Haven't read the actual paper, so I'm infering from the article, but basically the argument appears to be that under common beyond-the-standard-model theories,

Haven't read the actual paper, so I'm infering from the article, but basically the argument appears to be that under common beyond-the-standard-model theories, it's likely that most heavy particles are unstable. Instead they argue that it's likely to be a weak particle that just happens to not be interacting with visible light. By no means a novel idea as the article makes it seem. Don't take that as a jab against the paper though. It's important to constrain what we would expect under existing theories, both as avenues for future theoretical research and to guide experiment. Frankly, until one of the experiments see something the standard model doesn't predict, everybody's just taking shots in the dark.