Question about Sonnenkönig Fresco 180

According to the manufacturer's website, this unit is designed for rooms up to 77m3, but 115m3 are specified here. Where does this figure come from? I have generally noticed that square metre and cubic metre figures are often confused in air conditioners. I've even noticed this on manufacturers' websites (De'Longhi, for example). On the other hand, the figure on the manufacturer's website of "room size up to approx. 35 m² / 77 m³" for a unit with 18000BTU seems surprisingly low to me?