I went and re-watched the PBS Spacetime episode on neutron star collisions, and while he didn't address this specifically (at least in that episode,) there was an animation that seemed to show beams emitting from the poles. I think it's the case that the gamma ray emissions follow that pattern. IIRC, it has something to do with the magnetic field orientation. (I'm just a lay person entertained by cosmology, so not very confident.) Above a certain combined mass, neutron star collisions are one way that black holes form, so that would line up with what you said you read.