The model for 1D-projectile motion is the following:
x_(k+1) = x_k + v_k * dt + 0.5 * a_k * dt^2
v_(k+1) = v_k + a_k * dt
a_(k+1) = a_k
that in matrix from is the following:
1 dt 0.5*dt^2
0 1 dt
0 0 1
That is different from the matrix implemented in the example
// Discrete LTI projectile motion, measuring position only
A << 1, dt, 0, 0, 1, dt, 0, 0, 1;