Was this El Camino High School in Oceanside, CA by chance? I came here to say something basically identical - but realized you stole my thunder, since your son had a near identical experience. :)

All the smartest kids in my high school (including 1500+ SAT types) all went to UCSD/UCLA/Berekly. It wasn't until I was in grad school years later, and hung around lots of Stanford/Harvard/MIT grads that I realized they weren't really much smarter or harder working than all the kids in my high school, they just grew up with the expectation of going to a Ivy school ingrained in their experience.