You are right, the offset is not different. I was thinking the hub size was different for manufacturability. I don't know why it's different but it is.

Hub size can cause vibration. I am aware of this certain fact. And my comments are constructive - you are hiding information from your buyers. They are 18x8.5 +46 BMW Part No 6770200

Have you fit 18'' wheels on an X6? It may be possible, but it's not approved by BMW...