Angular momentum of an $N$-body system is of the form $Q(y,z)=y^TDz$?

I was reading in a book that the angular momentum of the $N$-body system is of the form $Q(y,z)=y^TDz$ with $y, z$ vectors and $D$ a matrix. But the angular momentum of the $N$-body system is something like $L=sum_{i=1}^Nq_itimes p_i$ no? How do you put it in the previous form?

edit :

I am not sure if this helps but it is the citation that is causing me trouble.

We next consider partitioned Runge-Kutta methods for systems
$dot{y}=f(y,z), dot{z}=g(y,z)$. Usually such methods cannot conserve
general quadratic invariants. We therefore concentrate on quadratic
invariants of the form begin{equation} Q(y,z)=y^TDz end{equation}
where $D$ is a matrix of appropriate dimensions. Observe that the
angular momentum of $N$-body systems is of this form.