Usually the FDS box is styrofoam that holds the Disk System, with a cardboard lid that fits on top of the styrofoam. In the case of this box, however, the styrofoam is entirely encased by cardboard. The box opens at the side. It's likely among the first releases of the Disk System.

The likely reason for the change in style is money. The box below requires a top lid of styrofoam and a bottom side of cardboard. The more typical FDS box doesn't require those things. That saves money.

This FDS box opens at the side, instead of lifting off the top lid.

The styrofoam containing the Disk System slides out.