I'm not sure about all the details but I think the answer might be
Where "walk" really means
Exit, in particular, in case of emergency.
If you can walk, I'll point in the direction you need to walk.
Where the airsteward(ess) stands, and is pointing, indicates the direction you should go to exit an airplane in case of emergency, as long as you are close to the front of the plane.
But only if you're close to me, otherwise I'll point in the opposite direction.
If you are near the rear of the plane then the emergency exit is in the back and you need to go in the opposite direction to where the airsteward(ess) is.
If you can't walk, I'll point out what needs to change before you can walk.
Some people will need to use the side exits on a plane. Often, I think the plan is for the cabin crew to manage the front and back exits and for the passenger in the window seat of the middle aisle to manage the emergency exits there. In this case the airsteward(ess) will point out to that passenger what "needs to change" for an emergency exit to happen.
This answer is quite loose but the idea of back, side and front makes me think that the answer is probably not far away from this.