He can hear the other set footsteps, but his pace hasn't exactly made his own particularly subtle. Still, he pumps the brakes enough that maybe the guard won't hear and abandon his task, getting ready to sprint forward again if either he turned around or the second he pushed the door open. Though he hasn't gotten to test the fact, he has it on good, precocious authority (Kevin's) that he can easily outrun a car driving around their neighborhood. Should be good enough to close the gap even if he's slowing now.