I think that's just it. The boy doesn't appear to be the brightest crayon in the box. I have no doubt that your girls have enough sense to know, in a situation like that, to go to a "safe" stranger (a cop, a teacher... my mother would always tell me when I was little to find an old lady and ask her for help, or a sales clerk, or some such). Either the boy just isn't very bright or he's making excuses because there's a deeper reason why he didn't want to be found.

Just an opinion based on what little I know.