Red: There's a large _something_ strapped to the character's back. Graves does not wear something on his back except for a cape. (What if he's just against a wall though?)
Green: He is holding his gun with one hand, almost as if it's some sort of pistol and not a shotgun. Graves fires his shotgun with _both_ hands
Orange: That hand almost looks... _Mechaical_
Pink: That weapon has recently been fired. Jhin's teasers loved to throw gunpowder debris all over the place. A Shotgun would just be smoking from the top of the barrel and he would more than likely still be holding it with two hands. From the way the character is positioned, his other hand can't possibly be on his weapon.
_What if it's an unmasked Jhin!?_ Unlikely, but there are signs.
Edit: Turkey ruined everything it's guaranteed Graves. I'm just as let down as you all are.