It was the flex bone or double wing- ran by most of the service academies now and Paul Johnson at Ga. Southern, Navy, and Ga. Tech and by my son's HS team 3-4 years ago. The wings are called A backs and the set back or fullback is a B back. It's quite common for one of the A backs to go in motion and often reverse course.
While an abrupt start may appear to be mimicking the snap, nothing about it is illegal motion-
Motion is a key component to the job a slot back must do. Since most motions are not called, the slot must learn when and how to properly execute these motions. The first motion, is the two-step motion, which as the name implies, means the slot will take two steps toward their aiming point before the ball is snapped. The aiming point is the heels of the B back, as shown in figure 11-7. The cadence is a rhythmic cadence which allows for the slot to leave at a certain part of the cadence, which was discussed in Chapter three. On two step motion, the slot, upon hearing the s in the word set should push off the outside foot, opening the inside foot to where the toe is pointing to the aiming point.