I have a feeling it has more to do with their existing proposal beside this lot. I know the city was taking issues about how tight the existing site was for 2 towers, so I image that they bought this to allow for 2 towers with a bit more room.
From my understanding, the Cuumberland Garage proposal, 2 bloor west, and 50 bloor west are alll being redesigned to work better together. Instead of 3 different developments being awkward, they are working together to create a sort of master plan for the area that will be developed in 3 seperate plots. I read somewhere that they want to introduce a view corridor to the historic firehouse from bloor..