Rude man at park

Ok so I'm babysitting this girl and she's 7. I was sitting on the benches while she played. She comes running up to me and says a man told her she can't walk up the slide. I asked her if there was anyone coming down, and she said no. I told her not to listen to the man he shouldn't be talking to you, but she didn't want to play anymore. She was too afraid to go back, she gets embarresed easily. This really mad me mad. I know she's not suppose to be climbing up the stairs but is it his place to tell another child what to do? Especially if his child isn't being affected ?
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Ok thanks guys I just really wanted to know if I should be mad or not. And I see he was in the right to tell her. I don't have kids or go to parks so I don't know. 
I just myself would not tell another kid what to do, that should be left up to the parent