It audibled the Cowboys into a zone running play.
The significance of the audible being Shanahan, of course, is in reference to Super Bowl LI. In case you’ve been living under a rock, the Falcons blew a 28-3 lead to the Patriots, after being up late in the third quarter.
The Falcons didn’t run the ball as much as they should have, hence the audible being called Shanahan.
There’s not many other code words you could use for the audible for the rest of the offense to easily remember what the audible is. But that one’s also obvious enough to where some of the Giants could guess. Because well, the Falcons should have run the damn ball.