A fisheye would also have bent the line of the glass at the top of the picture but it's perfectly straight. A wide angle was used to take the photo below, the rest I still think was rendered on top of it. As for support, there would still have to be a beam or something around the perimeter of the floor. Tempered glass just can't be used as it's shown here without being framed in. As a wall, sure, but not as an unsupported floor.