As you can see from the formation, the Bears are in a heavy package. There is a good chance they run out of this formation or are extremely worried about pass rush. 2 wide, single back, tight end in tight and an offensive lineman in a TE spot.
This leaves Alshon in one-on-one coverage deep coverage and the other receivers that ran the flat and a look off by Cutler freezes the safety.
Even though he doesn't make the catch, Alshon draws the pass interference penalty.
The two linebackers in the A gaps drop back into coverage
Both Bears players try to converge on the blitzer. As you can see this leaves the corner free to come down to the line of scrimmage.