Although both are members of the cactus family, they are not the same and not closely related. They do have some similarities, but not as many as you would think.
Night blooming Cereus (note the spelling) is a twiggy cactus with very small spines. It is known botanically as Peniocereus greggii or Cereus greggii and grows from a tuber. The flower blooms for only one night. It is native to the southwest US and Central America.
Night Blooming Cereus - DesertUSA Christmas cactus is an epiphyte (grown on another plant as it's host and not in the soil) with flat stems that resemble a leaf and does not have spines. It is known botanically as Schlumbergera. They flower sporatically. It is native to Brazil in South America. The variety Christmas cactus is actually a hybrid.
Plants Belonging to the Genus 'Schlumbergera' Newt