Yes, it is a private parking lot (parking for employees only), but it is open for public foot, bike and car access (how else are you supposed to reach the public charging stations?). I feel "permissive" is the correct value, because according to the wiki "On non-public roads / elements
permissive [equals] Open to general traffic [...]." and "private [equals] General public access is not allowed." Which is not the case here.