It is, sort of.

4WD vehicles with snow tires don't have to chain up at R-2, the most common level of chain control. Subaru hasn't sold 2WD vehicles in the US in 20 years, so the Caltrans employee's assumption is a pretty safe one. California considers anything with the "M+S" mark to be a snow tire, so virtually anything but high-performance tires or the silly rubber bands attached to ridiculously large chrome rim-like objects counts.

I got waved through in my Jeep every single time, and 2wd Cherokees were pretty common, especially in California. Sometimes they saw the block heater plug and waved me through, sometimes they squatted and saw the front diff, but usually they saw a Jeep and waved.