Even in summer when the battery is at optimum temperature without any electrical heating that is good going.
Not sure which generation of BMW electric drive train the Mini has but it must be a very recent one (perhaps 4th or 5th generation) to be able to turn in figures this good. BMW have been steadly improving the efficiency of their electric drive sub-assembly components using the i3 as a test bed. I have never got my 2016 i3 better than 5.5 miles per kWh. The Leaf before that would often achieve 5.5. mile per kWh in summer. Hoping for better when I switch to a bigger battery i3 without a REx.