The explanation for how Read Option Calls work...
Per Blandino:
"He is still treated as a runner until he is clearly out of the play. The quarterback makes the pitch, he's still a runner - he can be hit like a runner until he's clearly out of the play."
The quarterback and the running back, they're both treated as runners. We don't know who has the football, we don't know who's going to take it, so both players are treated as runners.
The basic concept is, the quarterback position is not defenseless throughout the down.
It's the posture he presents that will dictate his protections."
http://www.fieldgulls.com/seahawks-notes/2013/9/5/4699204/nfl-read-option-rules-quarterback-hits
Read option does not mean that the QB is a runner. They are a runner as long as they are in the play. Bradford clearly fades back and is not in a running posture. Suggs then proceeds to go for Bradford's left knee.
I also don't believe Bradford attempted to trick the defense. Bradford never feigned a run or scramble.