I don’t think they meant geographic size. In terms of population they’re around 9th, in terms of GDP more like 25th. They’re not Malta obviously, but they don’t really stack up against the big traditionally heavyweight countries by most metrics.

If the design capacity was 25000, it would mean that an assumption that 20% possible error would get you that range.

That seems like a decent “outside approximation” range. Yeah some 3 person apartments will have only 1 person, but some 1 persons will have 3