VNAV is selected or armed by pressing the VNAV button, not by cycling the autothrottle switch. VNAV in green means that VNAV is active. It is white when only armed. It is available below 400 feet on approach.
Understood. However, the A/T in this situation has been manually disconnected leaving VNAV still annunciated in green and the aircraft has been flown onto the ground. E/D speed is not usually zero, so _if_ VNAV is still shown in green after landing, will cycling the A/T switch reeactivate the A/T (as it does in the air) and have the engines spooling up to achieve E/D speed.
Possibly, results may vary according to flap position and reverser use.
(Edited for typos)