[petuniasevan]

It's the radar "signature" that is measured. This asteroid has the radar characteristics of a carbonaceous chondrite.

From a press release at a NASA website:

"1998 KY26's color and radar reflectivity showed similarities to carbonaceous chondrites, primordial meteorites which formed during the origin of the solar system, and unlike any rocks formed on Earth. They contain complex organic compounds as well as 10 percent to 20 percent water."

[Graewoulf]

Thanks for the prompt reply!