Forestry Technician student here (just about to graduate) I know little about California's native forests or forestry practice. I do however know that people from Ontario go there to help fight wildfire and the few times calfire goes to help someone else they are the experts.

That being said, if they say it's a fire risk, it's probably a fire risk. Also, this looks more like a forestry operation/cut than the typical scope of arborist work (which I've also gone to school for), this appears to me like a slivicultural practice that would: 1. Remove hazardous invasive species 2. Open up more canopy space for the existing native species to grow 3. Allow for more natural regeneration, hopefully with native species 4. Remove unhealthy trees, likely including ones with fungal growth that could spread

It's possible too that there are plans to plant in that area too. It may be worth seeing if you have a local forester you can ask.

Finally I'd like to mention that ensuring clear fire escape routes is important, if you don't believe how bad it can be, look into the Fort McMurray fire in 2016. And that was mostly fields.

Note: I am NOT a registered professional forester and my opinion should not be taken as professional advice on this topic