Family spat or modesty madness?

While taking my usual early morning walk on Saturday, I encountered three obviously orthodox Jews, almost certainly on their way to Shul.  A boy, a youth (late teens or early twenties) and a girl (similar age).  The two boys were walking together, while the girl was about ten paces behind.  The thought that immediately sprang to mind was, why don’t they walk together?  Is this a little family spat, or is this the latest form of modesty madness from the Meshugge Frum?