My read of this (I am a physicist by training) is that they’re possibly picking up radio emissions from triboelectric effects due to the enormous shear forces in a slowly motile ice sheet grinding over a quartz rich (east Antarctica has a high quartz concentration) substrate.

We’re talking about cubic kilometres of ice, moving jerkily with stick-slip motion over bedrock - the potentials generated would likely be in the megavolt range.

It would also explain the 30 degree incidence, as you’d expect the signal to refract within the ice and exit at a shallow angle.

In their shoes, I would be looking for correlation with seismographic events and high res GPS ice flow monitoring, not other neutrino observatories - it would seem wise to me to eliminate known physical effects as causes before invoking exotic matter.