He is not required to make up the prayer; because the initiation of the prayer is not valid at all, as intention is a condition for the validity of the prayer. If it is missed, the initiation is not valid. This is different from when he intends to pray but does not specify the intention for the voluntary prayer; because the voluntary prayer is valid with a general intention, so the initiation of it is valid. If he invalidates it and does not complete it, he is required to make it up; because the voluntary prayer becomes obligatory upon initiating it.