Starting from rest at a distance infinity, any object (regardless of it's own mass) necessarily undergoes a minimum increase in kinetic energy due to the gravitational potential of the mass of the target object (in this case the Earth, which has a known mass and so this is calculable). So I think the assumption is that the object isn't propelling itself away from the earth, and the object hasn't experienced any major competing gravitational forces inside the radius of the Moon's orbit.

Also, 11km/s isn't terribly quick on the celestial scale, I'd imagine.