I cannot comment on which course he should take next but I can give you some information regarding the UC’s and CC classes. My only advice about CC classes is to make sure he gets a good grade (A preferably) since any college course taken will be on his permanent college transcript.
If the CC class is UC transferable and taken the summer after 9th to the summer prior to 12th, the grade will be calculated into his UC GPA. Also the class will get 1 extra Honors point in the UC GPA calculation. The UC’s consider AP and CC classes comparable in terms of the extra Honors points and rigor.
Since he took the class in 9th grade, it will not be calculated into the UC GPA but it will be considered during the UC application review for course rigor.