The CNN article I cited was well-researched, but John53 is correct about the earlier (updated in 2023) factcheck article. All it did was change around some of the assumptions to get vehicle-related deaths above gun deaths. So your nitpick doesn't really tell us anything significant, if all you can do is squint at the data and quibble over which cause wins the gold medal for killing children. Obviously, one could also just say "leading cause of teenage deaths" to alter the results, as well.
I wouldn't argue with an attempt to strengthen vehicle safety laws as well as gun safety laws. The former would be less politically controversial in the US, apparently.