It is a designed play.
The receiver is to go down field and fake a short route (ie, a hook). The QB pumps as if to throw the short pass, hoping the DB will bite and commit himself to make a play.
As the DB commits to covering the short pass, the receiver takes off deep with (again hopefully) the DB caught flat-footed or moving in the wrong/opposite direction... "vacuumed" in (that certain word still censored???) by the "pump fake"
IMO, what both QB's need to develop is to look off the intended/initial receiver. Both have a tendency (especially Chang) to look immediately at the primary receiver, tipping off the defense as to where the ball is going.
I don't know if it's too late to learn or develop the skill at this stage, even though Chang is still a relative rookie.
IIRC, Matt Dunigan was excellent at throwing defenders off by the occasional mis-direction/look-off.
Obviously you can't do it all the time or the defense will know not to bite on the initial "look-off"