Likely because they were bullies, as it’s obvious that he tried to avoid the boys quickly/secretly. we know this because his heart beat increased and he hid himself away from the boys view.
They would do it because the officer would probably be pressuring them to tell an answer.
He is basically saying to get the real story before you turn them into a lie. Basically stating that you need to know the entire story before you make it into some fairytail of lies. When someone has the facts with concrete evidence you cannot twist it into a lie, thus it is stubborn; But statistics are easily twisted because they do not have the evidence to back them up, because they are simply statistics, not facts. Idk if this works but hope it helps!