AndrewSnow
I would ask deference to the local mapper. You will note that all of the local POI's and all of the Mapillary images in the vicinity are my contributions.  When I note building errors like this - I am standing on the sidewalk doing a field Vespucci survey.  Conditions are not the best - this is a rough neighborhood - so I apologize if the note was terse, but the problem here is that Mapbox's contract team, working as they did by pushing blocks of Lidar derived building outlines around, came to a problem where the long rear segment of the building to the west couldn't slide past the one on the east.  They "solved" it by created a virtual alley between the buildings - one that doesn't exist in the field.  If you live here (I do) you know that essentially all SF buildings are "zero lot line", meaning there is no sideyard space between them.  The building thus need to be "connected".