He IS very quick to lead the child away. He may have had good intentions but that is not a sensible way to deal with the situation.
I once came across a young girl, about 5 years old running past me in a busy shopping centre, something about the fear on her face as she ran past me made me stop her. I was with my three children who were only a little older and was aware that I was more likely to appear a "safe" person both to her and to other shoppers. We stayed still, I was very conscious that I should not touch her and I asked her if she was alright.
She had lost her mother, panicked and started running around the shopping centre. It was clear that her mother was nowhere in sight and so I felt that it was best to return to the place where she had last been with her mother (Marks & Spencers) to seek help.
At that point she said that the two year old boy standing 10 feet away looking at a shop window was her brother who was also lost! I would not have even realised that he was also lost.
I told the sister to hold her brother's hand and to stay close but did not touch either child. I talked to them fairly loudly for the benefit of passers by about how they were lost but we were going back to the shop so that they could put out an announcement asking for their parents. I felt quite uncomfortable leading them away but didn't see that I had much option.
That all took about 10 minutes and I spent a lot of time talking calmly to the child to establish the situation and determine the best way to deal with it. It would have been obvious to everyone within 10 feet what was happening.
I would expect anyone who found a lost child to look around and speak to people in the immediate vicinity before taking them away to find help. I would also ask them, "Where is your Mummy or Daddy?" The child is old enough to point at his mum if she's around, as indeed she was.