I'm not certain. One similar disease that is known to affect Guava (Psidium spp.), including Strawberry Guava (Psidium cattleyanum), is Guava Fungal Leaf Spot (both Pseudocercospora psidii and P. sawadae). This is a disease associated with humid, warm weather. If Pseudocercospora is the cause of the leaf spots, perhaps the infection was triggered by California's unusually wet Autumn.
Control in commercial plantations involves application of copper-based fungicides. There is also another disease: Guava Algal leaf Spot (Cephaleuros virescens), which is caused by a pathogenic algae. Those leaf spots usually look somewhat different however.
Besides fungicides, such diseases may be lessened in severity by regular removal and disposal of infected leaves.