They say the rooms are 1DK, but I have to question whether the rooms have the kitchenette, we never see one from what I remember. The description of what such an apartment would look like is a bit off as well; it'd be 1 room with a kitchen or kitchenette and space for dining, which may or may not be separate from the bedroom. If you've ever seen an anime/manga dorm room, that's still an 1DK, and something just a bit larger might be an 1LDK. Some might consider that as two separate rooms, with the counter serving as the wall, but I would not. There are some single bedroom apartments in Japan that do separate the bedroom, but they tend to be newer and on the more luxurious side, older single bedroom apartments almost always combine everything into as few rooms as possible.
Looking at the rest of the building as we can see it, the rooms are probably more consistent with the older style of 1DK, with everything except the toilet (and shower/bath, if they have it) in the same room. This would also explain why we see Shiori sitting seiza next to the bed to eat a page later instead of eating in her dining room.