We don't know for sure but he did two things. First he called an alert, then he clearly behind his back signalled to the left.
If it was a run to the right that he just flipped he would not have needed both signals. I am 99% sure he checked out of a pass into a run and to the wrong side. Poor check.
I then think they rushed the 3rd down not sure why they didn't take their time on that but was an odd call.