The data is unfortunately not granular enough. It combines "reserved spots" and garages. A reserved spot could be an open parking lot with an assigned number. It doesn't help with the charging at all.

I'd guesstimate that the cars parked "american style" (in a private garage or on the driveway of the house) in Europe is < 10%. You really need to live in a small town or a village to find these setups.