If we determine that the player "lurched", we have a false start. IMO, If any other movement would be legal if the players was shifting (e.g. turning upfield and stopping in a new position), we wouldn't have a false start. Therefore, the turning upfield early (without a lurch) seems to be a violation of 7-1-4-b (below) if the player is "moving toward the opponent's goal line" at the snap.
b. Man in Motion.
1. One back may be in motion, but he may not be moving toward his opponent’s goal line.
2. The player who goes in motion may not start from the line of scrimmage unless he first becomes a back and comes to a complete stop.
3. A player in motion at the snap must have satisfied the one-second
rule—i.e., he may not start his motion before any shift has ended (Rule
2-22-1-c).