They are basically talking about a similar idea to a "star" grounding arrangement, where
you want to avoid inductive ground loops which can cause noise, oscillations, and
magnetic-field inductive transmission. Since the ckt is using an inductor as its major
component, you don't want it inductively coupling willy-nilly [FYI, a rigorous engineering
term] to any other part of the ckt, such as an inductive ground trace.http://www.lh-electric.net/tutorials/gnd_loop.html
Check here for nice spaghetti designs,http://www.google.com/search?q=star+grounding&hl=en&tbo=u&tbm=isch&source=univ&biw=990&bih=824&sei=4k_rUOvZFaaZiQK1koGYBQ
Strictly speaking, a ground shift problem involves the current through a trace or wire
causing a voltage shift due to the resistance of said trace|wire, which appears on the ground
of another ckt which is wired in a daisy-chain fashion off [ie, downstream] of the first ckt.
Simple V = I * Rwire. Also, at high-frequencies, the inductance [impedance] of said trace|wire
also becomes a factor, ie V = I * Zwire. So, the star wiring arrangement is intended to
eliminate such daisy-chain wiring.