I beleve what he is saying is that if they had used 16” wheels like the Brompton their fold would be smaller. But they have gone with larger 24” wheels for better durability and ride.
Going by those dimensions, Brompton takes 89l of space, whereas Helix takes 85l, so I guess they meant the overal volume when rounded up to a containing box.
Can you clarify what you mean by “the fold is the most compact possible, even more compact than Brompton in terms of maximizing the use of space“
The Brompton's folded size is 585mm high x 565mm long x 270mm wide
The Helix is 580mm x 635mm x 230mm.