By definition does a murtad needs to be a muslim first by sure belief and knowledge and then reverts from Islam or anyone who is just known as a muslim and not even a practicing one and then reverts. An example is a kid who is born in a muslim family and by tradition follows islam since childhood due to his parents being muslims but as he matures like at the age of 17-18 he becomes an atheist since he never understood Islam anyway. Is he still considered a murtad?