After researching this a bit, they also get jury summons prospects from the DMV.

So where exactly do jury lists come from? A spokesperson for the San Diego Superior Court told News 8 that their jury pool does come from voter registrations, but they also get jurors from the DMV.

So, we can verify that jury candidates are selected from the voter registration list, but the implied concern from the email - that 449,000 people have illegally voted - cannot be verified because all or some of those names could have come from the DMV where non-citizens can legally get a driver’s license.

https://www.cbs8.com/article/news/verify/verify-are-hundreds-of-thousands-of-non-us-citizens-voting-in-ca-elections/509-9a73d20f-c9e1-42ac-a475-24afb5c12259