Were you standing in observation mode in an empty street? If so the slightest movement would have attracted your attention.Imagine you are in a Paddle field (20 meters x 10 meters) at night, with a sodium light but enough to see a person quite well. I was there alone at night, and a cat apperaed and called my attention. In any position at least one of the two (GM or JW) would see JT.
Don't know about anyone else - but when I am in conversation particularly face to face with one other person - my attention is on that person and what they are saying I don't think I would notice a passer-by on the periphery unless I had to move out of their way.
I never stand and look around me I think basically that would be a rude thing to do if the topic of the conversation was not about something which had happened or was happening at that spot.
With the benefit of hindsight GM would never have checked on his children and went back to his meal and JT would have raised the alarm.
My opinion