only a guess, but the buttons on the steering wheel of a M5 have M1 and M2 on them and are used for other things. On non M5 where those M1 and M2 bittons are those for defining the distance to the car in front.
I've never noticed a M5 with the radar housing in the grill below the bumper.(Its a square thats sort of recessed below where the number plate would be)
In fact I've not noticed any cars otehr than my own that have ACC, seems a rare option at least in the UK - at least by my own observations