I reckon passersby should *ask* the person if they are okay, absolutely, every time. But when the person is capable of saying they are fine, and assuming there's no pool of blood or limbs bent the wrong way, passersby should accept that it's Not An Emergency and move on with their lives. Maybe say something like "is there anything you need?", "are you going to be able to get home ok?", or "is your GP aware? Maybe an appointment wouldn't be a bad idea," but don't insist on calling out a full emergency ambulance.