The Segway is quite large and needs parking or storage. Also, it can't go up stairs. Hoverboards can be picked up and carried easily around an office or home, and can be tossed under a desk or in a backpack for storage.
A Segway is like a bike in that you always have to be thinking about where to put it when you arrive. Hoverboard is much more like walking, in that you can toss it in your backpack or just carry it when you arrive.
The immediate use case I thought of when reading about it was that you don't have to worry about where to put it. You ride it to work then the robot pops up its cute little face and it drives itself back home. Then it's waiting to pick you up when you're done. Obviously, that would depend on software that's probably a lot more advanced than the current prototype. But I suppose that's why they're soliciting developers.
A Segway is like a bike in that you always have to be thinking about where to put it when you arrive. Hoverboard is much more like walking, in that you can toss it in your backpack or just carry it when you arrive.
Though I'd rather just walk.