The foil might be the same, but that doesn't mean everything is. I've had generic raisin bran cereal that was clearly Kellogg's in a different box, excpet that 1 out of 100 boxes had a slightly different flavor that wouldn't have passed Kellogg's quality controls but since still food safe (so I assume) the generic boxes got it. Of course when doing a private labor you can specify the higher quality controls, but that comes at a higher price. Most of the time Kellogg's is going to make the same cereal either way so nobody can tell the difference, but when something goes off in the process the cheaper generics get it.

My knowledge of foil suggests there isn't anything Reynolds could to that would reduce quality that would still be good enough to ship.