Half the DNA on the NYC Subway Matches No Known Organism

>The problem, though, is that our genetic libraries are still incomplete. For example, if I don't know what the DNA sequences of a cockroach look like, how can I know my DNA sequence belongs to a cockroach? That's how why half the DNA found in the project matched no known organism.

This is the crux of the article, file under "click-bait".

Cowabunga?