This is a foul, there was an editorial change in this year's book to confirm that this is indeed a shift, and if the WR does not stop, then it constitutes an illegal shift.
The editorial change:
2-22-1-a - Inserted the words "or stance" in the first sentence.
ARTICLE 1. a. A shift is a simultaneous change of position or stance by two
or more offensive players after the ball is ready for play before the snap for a
scrimmage down (A.R. 7-1-3-I-II and A.R. 7-1-2-I-IV).