Cal Poly recomputes GPA based on courses taken in 9th - 11th grades, with a capped maximum of 8 weighted semesters (honors / AP). Because weighted semesters are capped, a student with a high number of courses taken can end up with a lower capped weighted GPA, even if they took a lot of AP courses, etc.
Here’s another thread with some discussion: Cal Poly SLO Capped GPA - calculate
Cal Poly doesn’t yield protect. However, it can sometimes appear that way to applicants, because a “high stat” student might not have the highest SLO GPA.