Clarification needed on Encroachment vs Ilegal Motion

[WyMike]

Originally posted by ABoselli
False start in both cases.

Whether he was in the NZ doesn't matter, because he feigned the start of the play, which whether he's 8 yards off the line or right on it, is a false start, dead ball penalty.

Isn't 'feigning' more or less sudden movement without the intention of actually leaving? Simplified & Illustrated page 59, 7-1-7a states, "Jerky movements which simulate the beginning of the down or acts clearly intended to cause B to encroach are false starts."

In the above examples the receiver is definitely leaving early with no intentions of 'feigning'. Is this splitting hairs and am I reading too much into the rule?

False starts, feigning, would be a dead ball foul. But could it also be interpreted as an illegal motion/shift? This is where I get confused by the language of the rules relating to each.