The way the architect explained it last night was that they looked at the original Union Station complex of both headhouse and concourse: one building neoclassical and one more industrial/Crystal Palace in feeling.
Thinking about that exposed structure led them to look at "Second Chicago School" solutions. There are a couple of hops in that logic, but that was the explanation.
I think Lynn Becker is very much on point with his description of the design as "viable." As in
what depth is required to make double-loaded corridors of apartments viable in this envelope of space. That depth is what forces the cantilevers, which in turn requires the beltline floor.