https://admission.universityofcalifornia.edu/admission-requirements/transfer-requirements/ says that “You’re a transfer student if you enrolled in a regular session (fall, winter or spring) at a college or university after high school. (Taking a class or two during the summer term immediately following high school graduation doesn’t make you a transfer student.)”
For most purposes, it is more desirable to enter as a frosh than as a transfer, since a frosh has the option, but not the obligation (based on credit limits or FA/scholarship duration) to graduate in two years (or other duration lower than four years). Frosh also have more flexibility in changing major than transfers who are at the junior level.
If you want to apply as a transfer student, you may want to ask UC directly if that is allowed based on college courses completed during high school (you need 60 semester units as well as various subject requirements for UC, the campus, and your intended major).