Really all I can say is "all's well that ends well." You weren't hurt, he wasn't hurt and above all your child wasn't hurt.
You did get a scare, but that is no bad thing: reminds us to be vigilant.
However, looking at the story there are nothing but assumptions about his intent, so no I can't say that drawing would have been a good idea.
The only things I could say about him based on the event as described is that he was a wind-shield cleaner with a bit of goth fashion-sense who decided to do you a favour or has a personal intolerance of dirty side-view mirrors.
I think you did well, precisely because you did listen to the voice in your head, yet didn't over react by drawing just because someone is a bit odd. If he was a guy up to know good, your body language would have been screaming "I'm not a day dreamer thinking of other things, I'm already aware of you". Next time you clock someone that trips your alarms, though, keep a closer eye on their advance!!