This a Feature of the Clinton era Motor Voter Law, not a Bug.
Under Motor Voter, if you register for something like a driver’s license, you get registered to vote. If California is issuing DLs to illegal aliens, then it is a safe bet they are getting registered to vote as well.
Interestingly, when I recently moved to AZ, I got a notice from previous State I was no longer registered to vote in that State.
With all the moving around I have done in the last 30 years, that was a first.
Glad to see it!
it was a Blue State too.