The title is a bit hyperbolic. The article shows how the Van Allen belts constitute a "nearly impenetrable" barrier preventing "ultra-fast electrons" from approaching the earth.
In fairness, the article is almost as bad as the title. It isn't even clear at first that they are taking about belt electrons rather than cosmic-ray electrons, which have many orders of magnitude higher energy.
The gist of the article seems to be, "The sharpness of the outer edge of the inner Van Allen belt is due to scattering of high-energy belt electrons off cold plasma surrounding the Earth" but it's really difficult to tell.
