Take it easy, he's a Junior and he asked. If you went to the startline of a Cat 5 race and asked the riders who read the rulebook you'd get about half of the riders to say they did, and that's after telling them it's required that they do so (this was at a Cat 5 clinic that I ran). Based on some questions most of those half just skimmed the rulebook too.
As a Junior I also only skimmed the rulebook; I was lucky enough to have an understanding friend (a Junior also) who demonstrated to me that I didn't know enough simply by asking me a few questions.
On the other hand there are a lot of Junior specific rules. Juniors should know them inside-out, especially the differences between the various age groups.