An Interactive Look at Zoning in the Sloop

You know we love interactive maps here at Sloopin and yesterday stumbled upon one that details city zoning (via the website secondcityzoning.org):

While most things are relatively predictable in relation to the Sloop, one thing that we found strange was that the swath of blue in Grant Park where the uncovered train tracks currently run.  Apparently this is zoned DX-16:

In case you're having a hard time reading the image above DX-16 is described as:

Downtown high-rises - offices or apartments - with ground-floor stores. Prevalent on the edges of Loop: east of Dearborn Ave, in River North, the South Loop, and the West Loop.

While we doubt we would see a high-rise go in here, it still seems strange.  Do we have any zoning aficionados who have some perspective on this?