You can get this effect by dropping into one ring then travelling to another ring. Your velocity will remain relative to the original ring. This is a similar effect to dropping fairly close to a station but with your local reference frame still being linked to the planet it orbits rather than the station itself - you can target the station but it may be zooming away from you faster than your ship can go.
This may also be linked to an existing bug in the game that has made it into beta too where you can drop into a USS, CZ or other instance and have it zoom off at hundreds of m/s because you are not in it's reference frame (your velocity is relative to something other than the centre of the instance).