The title of the article is a little misleading, I think. Whistlers (Right had polarised waves parallel, or slightly obliquely, to a magnetic field) are a standard part of MHD theory, and are known to travel faster than the local Alfven speed for short wavelengths
See http://farside.ph.utexas.edu/teaching/plasma/lectures/node51.html
The new thing here is NOT the speed of the wave, it is the mechanism that excites them, where the full kinetic description of what is going on in a shock front needs to be taken into account
