Virtually all reasonable alternatives to GR have been strongly ruled out, including theories with large extra dimensions in them. In general, these theories have a some kind of parameter which measures their deviation from GR, which is being squashed to zero. There's also just generally no reason to think there are extra dimensions at all

This article brings up neutron stars being slightly larger than expected, but the reality is there's no real expected maximum mass for a neutron star - because the equation of state and physics for neutron star interiors is unknown. The spin, and magnetic field of a neutron star can also serve to increase the maximum mass of a neutron star, which are very hard to model as there are no analytic solutions to a spinning body (nor an oblate body)

There are too many approximations in the paper to even come close to saying that the brane model explains this better than standard physics, and there's no reason to think that this event isn't explainable by standard physics