Does it help if you think of it as an alloy of metal and air?
When you make steel all you are doing is forming various crystal structures, and grains. Martensite, Ferrite Austenite, Cementite, etc. They are all the "same" material (iron and oxygen and carbon), yet if you figure out a new way of arranging their shapes "just so" you can say you invented a new type of steel.
This is the same way - they figured out a new way of arranging the atoms, so it's a more or less a new material.
(I do see your point of course, and this is more macroscopic than grains in steel, but I think it's not unreasonable to call it a new material.)
When you make steel all you are doing is forming various crystal structures, and grains. Martensite, Ferrite Austenite, Cementite, etc. They are all the "same" material (iron and oxygen and carbon), yet if you figure out a new way of arranging their shapes "just so" you can say you invented a new type of steel.
This is the same way - they figured out a new way of arranging the atoms, so it's a more or less a new material.
(I do see your point of course, and this is more macroscopic than grains in steel, but I think it's not unreasonable to call it a new material.)