Fine, then I pose to you the same problem description, with the added fact that the stranger is proud of having a boy, will only draw attention to a boy and wil

Fine, then I pose to you the same problem description, with the added fact that the stranger is proud of having a boy, will only draw attention to a boy and will thus say "at least one is a boy", independent of whether the other is a girl, while he would never say "at least one is a boy". You can't solve a logic puzzle by arguing the psychology of a persona depicted in the puzzle.