Good job, OP.

I would of grounded him anyway, and like someone suggested, have him read "the boy who cried wolf" for a lesson.

boring! you suck, op, for not even grounding the little bastard! if my kid did that, I'd spank him in front of all the other kids!

But that only works if they aren't being actively chased. If they are it helps to yell out something that's widely known so people with enough guts will help... Or at least someone will look in that direction and the "stranger" will be less likely to keep following.

No, I'm British and my parents/school taught us Stranger Danger too. It's a common thing although some countries may not have little things in school about it so it's mostly the parents' responsibility to teach their children.