I am not going with my "gut" Red, I am going with the burden of proof. If the school challenges the enrollment in that district the school has to prove it. If mom owns the condo, and the utilities are in her name, then its going to be difficult for the school to meet their burden of proof. For example, since my daughter and grandchildren live with me, I have to provide the schools, on a yearly basis, proof that I own the house, and a couple of utility bills in my name. I have to certify that my daughter resides there (because I own the property).And as usual, LdiJ, you are going with your gut, not the law.
While Mom might use her documents showing ownership as the basis of registering, the fact is, she and the child do not live at the residence she is using for the purpose of school registration. According to California Law, the parent/guardian has to be a current resident of the public school district, where current resident is as defined in CA Gov Code 244 and CA Ed Code 48200 and 48204.
Even a temporary relocation outside of district boundaries subjects you to disenrollment.
I've noticed the Palo Alto District School District even has a "Suspected Residency Violation Form" at https://www.pausd.org/registration/residency-important-information (Just an example within OP's state.)
So no, according to CA law, Mom is committing School Enrollment Fraud; the boy is enrolled in the wrong school, and can be, upon a district investigation revealing this, disenrolled. I do not know if there are any greater consequences in CA than this (fines?), but I suspect it depends on the school district.
I will note, the "Varsity Blues" college admissions scandal highlights what wealthy Southern Californians would do to help their children get an "educational advantage". Were it perfectly legal to enroll your child solely based on where you happened to own property, not where people actually reside, there would be a cottage industry of people jointly investing in properties for the purpose of school registration.
Yes, its quite possible that mom is committing school enrollment fraud, and maybe even a guarantee that she is (although we are hearing a one sided story) however, it still has to be proven and my point was that it could be difficult to prove.