Rude parenting advice from a stranger?

I'm a young 21 year year old mom. I'm pretty short as well, not even 5 ft. I went on a walk this morning to the park with my 3 year old son and my 4 year old nephew. Although my sister thinks I'm ridiculous for this, I make all three of us hold hands to walk, and stop every time we see a car. I make it very clear before we leave what the rules are, and that I have to be the one who walks on the outside. My son has ADHD and doesn't listen sometimes which is why I make it very clear. Anyway, we had just gotten back the park, and were walking on to our street. I made them walk in a line, with me being in front, and my nephew holding my hand (throws a fit if he isn't, and my son is usually very good at holding on to his cousins hand) I watched him very carefully, turned to answer my nephews question, then turned around and see my son had let go of his cousins hand and was standing behind me, instead of on the inside of the road. There wasn't any cars coming, but I still want him to know it wasn't okay, so I began to lecture him by yelling his name, and some woman walking down the street started screaming very rudely, "YOU KNOW, YOU SHOULD BE ON THE OUTSIDE OF THE ROAD AND THEY SHOULD BE ON THE INSIDE." I Was very angry already by the tone of her voice, but calmly said, "I know." I went to say "that's what I was about to say to him before you interrupted." But she interrupted AGAIN and yelled "WELL THEN WAKE THE F*** UP THEN!" I grabbed his arm and walked home.