Keith is actually half Altean and half Galran His mother being Altean she was in love with a Galran before Zarkon rose to power. Soon enough Keith was born and for about 10 years everything was fine, Keith lived happily with his mother until planet Altea was attacked. In a last resort to save her son his mother put him in a Cryopod, sending it towards earth, hoping to be able to save her son who would've surely been executed. The Cryopod crashes in the middle of a desert and is damaged to the point where Keith stays in stasis for 9,992 years. After he wakes up, looking human enough since he's only half Altean it's easy for him to pass as human, he's raised by a nice Korean woman who soon passes after. Because of his Altean blood he's able to unconsciously mimic others features so it isn't hard to convince people he's part Korean, therefore human. His Galran blood isn't revealed until later, as its been dormant for the longest time.