Did the “Giant of Kandahar” consume the missing soldiers because he needed the nourishment, or because human is a delicacy and this poor “creature” couldn’t contain himself and maintain any kind of personal discipline?

This was strictly done to preserve his life and was a matter of course for him as they regard humans as first of all a food source. That is their greatest value to the Anunnaki other than as slave labor. So it is not so different in how people view cattle. They are a premier food source for milk and meat, but oxen, for instance, can be beasts of burden and trained to serve in that way. Humans by virtue of their greater intelligence have more utility as slaves to do useful work than would be the case with an animal of minimal intelligence or trainability.