Give him a break. The bike laws have a lot of nuances that are hard to convey in a couple of seconds.

As a general rule, far more often than not, it's illegal to ride on the sidewalk.

In my city, it's generally legal. Unless you do it "dangerously" (whatever that means). The next city over, it's completely illegal. In the city in the other direction, it's legal so long as you don't do it in a "business district," which is defined as an area with a certain density of retail, restaurants, etc. (as if anyone could track the density as they ride). In yet another nearby town, it's illegal unless you're under a certain age and are just learning to ride (so parents can teach their kids on the sidewalk). Maybe he should have explained this to the driver while they were waiting at the light?

While these laws vary wildly from jurisdiction to jurisdiction, most cyclists are best served by just accepting as a general rule that sidewalk riding is usually illegal (which it is). I don't see anything wrong with telling a driver this general rule.