Perhaps his security guys called 911, but so far LAPD says they have no record of the event. I'm wary of trying to draw any conclusions about the event absent some independent confirmation.
I'm not sure police would be eager to investigate "some guy followed me" type of complaint. Of course, if the complainer knows the right people, they would. But Musk is squarely in the "wrong people" corner with the powers that run LA now, I think, so not sure he'll get a lot of help from LAPD on this.