I just found the kidney grill on the passenger's side to have this same problem while washing my car the other day. And like yourself, I said WTF when I barely pulled on it and it came off
. I don't know how it had not fallen off while driving down the road.
All my clips were intact upon inspection as well, but the black piece it snaps to kept moving back, not allowing it to clip in. I was going to take off the upper radiator shroud so I could reach the back of it, but then I realized my finger would fit through the grill.
Try sticking your index fingertip through the grill in order to pull the inner black piece toward the kidney grill/back of bumper (don't go past the first knuckle or it might hurt on the way out lol). Then while you are pulling the black piece toward the kidney grill with your index finger, support your thumb on the kidney grill's rim and push (causing a squeezing motion between your index and thumb)...you should hear a snap. Work your way around the perimeter sandwiching the bumper between the two pieces, and ta-dah!
