TBH these feel like a pretty typical refinements as an early design approaches a buildable state. I don't have any insight into the rationale, but it would be surprising if we didn't see any changes like this as KPMB iterates on the design. (For what it's worth, I think the changes are fine and the new iteration looks very nice.)
Exactly. When most initial renderings are produced, the projects aren't at the stage where specific materials -- as in, the actual product number from an actual extant supplier -- have been selected, so there's always going to be something of a delta between render and reality that has little to do with value engineering.
Typically, a renderer will get from the architect/developer some photographs of the site, and a preliminary set of drawings/plans that somewhat resembles those that you'd find in a typical rezoning package (site plan, elevations, context plan, maybe a SketchUp model, and possibly some low-fi renderings from the architect itself) and then the renderer interprets that set into a series of drafts that they then iterate through discussions with the client(s). You can of course render literally anything, without consideration of elements like structural engineering, utilities and servicing, cladding product availability, etc., but the general idea is to put the best foot forward in terms of the overall intent of the design.
That's why you never really want to read too much into renderings.