scannon....I don't know if it is true or not but the Navy / Marines do have a training area (Military Operating Area) just up the coast from Oceanside, Ca. called Camp Pendleton and they due do low level flights in the MOA from time to time and the area is pretty desolate even though I-5 dose run down the coast across the base.
I cannot say if the F-18's are armed for defense all the time but I would not doubt that they could be especially today with all of the new policies that have come about since I retired in 1990 from the Navy and Military flying (20yrs, 3months, 28days active duty, 13746hr of flight time) but if you read the original post you will see that it said they were on a training mission and they could have practice rounds and armaments on the AC which could do what is stated.
Just my thoughts and in no way any real idea if it is a true story….but I could see it happening.....
Here is a photo of the area.