I don't think the man did anything wrong , but I also think he would have done something better had he not approached her, especially if she was obviously a minor. By which I mean, you say she's tall-if she wasn't obviously wearing school uniform, had a hood up or could possibly have been in work uniform or, he approached her from her back view, could he have thought she wasn't a child but a grown woman?
He may have been lost and late and desperate to get directions. He may have thought she was a woman rather than a young girl. He may have just not been quite as perceptive as many of us and not realised that he may make her nervous.
But if you say she's normally a confident girl and she felt uncomfortable, is there any reason for this? However small?
I ask this because I remember several times being asked for directions (by men!) as a child/young teen. I remember sometimes it affected my day negatively, and sometimes it didn't bother me at all and I was happy to help or sad that I didn't know how to direct the man.
But then in the same way that some people appear dodgy when they aren't and some people appear cold when they're actually nice, and some people appear rude when they're shy, just because he made her feel uncomfortable doesn't necessarily mean he wasn't innocent.
It's sad, but if I was a man I think I would not have approached a child in this situation. Even as a woman I don't know if I'd approach children to ask for directions! Not just because I may make them uncomfortable but the child could take me the wrong way and I could end up in trouble. Sad but true.
On a sort of similar note DP has said that a while back some local children would knock on the door asking to come in and see our dog. He would always take the dog out the front on the lead for them, never letting them into the house or (back) garden because he was scared people would talk. I think that's really sad. But I understand why.