Impacted schools in LA school personnel do visit the child’s home and they often target the Hispanics. In Irvine schools they look the other way because the illegal Chinese kids help raise school test scores. Irvine schools do not want to send away the smart kids.
More likely it is due to a lazy administration that doesn’t give much of a crap. Plus, Irvine is pretty accepting of kids who want to transfer in (in general) usually the more difficult part is getting the home district (i.e. TUSD) to give the child a waiver to enroll in Irvine.