Well, technically there is an aspect of the underlying network protocol called time-to-live or TTL. Unless manipulated this value is decremented by each device

Well, technically there is an aspect of the underlying network protocol called time-to-live or TTL. Unless manipulated this value is decremented by each device in the chain on devices between your phone and your carrier. When tethering this value is then lower than it would be if the traffic were source from rather than through your device. Thus, the manipulation to which they refer typically refers to manipulating this value.