This seems to be what we used to refer to as a bedsitter, that is, a one-room flat with facilities. Micro apartments are purpose-built and new so they are glossier than the old bedsitters. Or you might think of them as similar to college accommodation where individuals have their own room (with ensuite), which is rented in the case of the college but bought in the micro apartment world. There are shared spaces for communal activities, creating, as the ad blurb says, happy micro-communities. There is no reason really why the spelling shouldn’t be microappartment but there seems to be resistence to it.