It's bad wording for sure. What they mean is that if the baby is traveling as a lap infant (with no assigned seat), you can request a seat (for free) for the baby if there is an extra one on the flight. If you want to have the baby in the "free" seat during takeoff and landing and when the seatbelt sign is on, you will need to bring along an FAA approved carseat to put the baby in. We usually did this or bought a seat for the baby. From what I understand, it is actually quite a bit safer to have the baby in a carseat rather than just holding the baby.