This is how they police by consent. Just because it goes no further than engage and explain doesn't mean no crime was commited.
Police spend in ordinate amounts of time in shopping centres taking this approach with teens (usually outside Boots!)
Just because none are officially cautioned or prosecuted doesn't mean what they did was legal.
They have said may have breeched. Well it's retrospective so they have to say that.
But they also said if he was stopped at the time he would have been spoken to at the time it probably would have invited intervention.
Whatever the point he didn't completely follow the guidelines as they argued he did.