Apparently the order of candidates is chosen by a lottery-style drawing of letters under a system that has been in place for almost 50 years, so Trump supporters can't really claim "election interference" here - if alphabetical order made a real difference you'd probably see a lot more fringe candidates with names like Aaron Aardman. The order of letters is also rotated by district so the candidates aren't in the same order on ballots across the state.
On the 82nd day before an election, the Secretary of State conducts a randomized drawing of letters of the alphabet pursuant to California Elections Code section 13112. The resulting order of letters constitutes the "randomized alphabet" to be used for determining the order of candidates' names on the ballot.
This procedure was established by legislation passed in 1975 in response to court rulings declaring that standard alphabetical order or incumbent-first was unconstitutional.
Find out more about the "randomized alphabet" used for determining the order of candidates' names on the ballot here.
www.sos.ca.gov