In general, the off campus events are helpful in providing information about the university, but don’t give admitted students as much of a feel for the campus culture.
Unfortunately, multiple California universities decided to have their admitted student day on April 13. If your student is considering two schools, attending a local UCR event and then an admitted student day at another university might be your best option.
Don’t be surprised if your student decides to enroll at the school where they attend the admitted student day. If you (as a parent) have a preference, I would make it a priority to visit that school’s admitted student day.