That could definitely apply to a lot of the examples they presented. I'm still mystified by Washington D.C.: they already had a higher murder rate than the US average, then handguns were banned in 1975, then their murder rate tripled while the national average stayed fairly flat, then their murder rate came back down to its mid-70s level in the late 2000s, then the handgun ban was struck down. My current favored conclusion from that is "gun control laws themselves just don't matter very much, and are dwarfed by other social and cultural forces."