Although I personally don't think the encounter as described would have given me a bad feeling I understand listening to your instincts....but it is no excuse for rudeness when there has been no harm inflicted. We may not like that he is slovenly or called out to a child....but he hasn't done anything to merit the treatment he got.
Again - I don't think the OP was intentionally rude but freaking out whenever an adult speaks to a child? I think it's a shame that we have gotten this way....seeing evil intent in almost everything.....and frankly that's a "hinky meter" that isn't working well. It's not that I think we should never listen to it....but that I don't think it is necessary to have the default setting so high.
Beautifully put, gen xer. You, too, Surianne.
OP, I'm sorry, but I have to agree that you were extremely rude to this guy who was just doing his job, and, in my opinion, not at all inappropriately. His JOB is to sell ice cream to kids. Calling from the truck and asking a potential customer, including a child on a porch although there is no adult in his sight line, if she wants to buy his product is not at all inappropriate -- and I doubt you would have thought so, either, had he been groomed and dressed like a country club member. In fact, if your daughter and her friends ever set up a lemonade stand on the sidewalk, I bet they do exactly what all the kids in my neighborhood do every time a neighbor walks, bikes, or even drives by: "Lemonade! Want to buy some lemonade?"
I won't argue with your "hinky meter" or comment on judgmentalness or snobbery, because I wasn't there, and your instincts are your instincts. Nevertheless, no matter how loudly your meter was ringing, I see absolutely no justification for your rudeness to this guy, and, yes, I understand you weren't abusive -- but you were unjustifiably rude. I'd be surprised if he didn't immediately feel that you were seeing him as a molester or kidnapper. If you want him not to try to sell to your daughter again, you can ask that politely. "No, thank you, and please don't try to sell to her again when you don't see me present. Thanks."
I agree with the poster who said that the way you handled it makes him less likely to consider that he may be dressing or selling in a poor way, and more likely to see you as a meanie who thinks she can bar him from the whole block. His "hinky meter" may have been going off, too, you know, explaining his hasty escape; for all he knew, you had an emotional imbalance and a gun.
Finally, I think you have some repair work to do with your daughter, who witnessed your behavior. It's fine to explain to her that you are so concerned for her safety that you behaved in a way that now you are sorry about. But I think you should make sure to un-teach what she surely learned about judging people by their appearance, respect for the dignity of working people who aren't as lucky as she, and rudeness when courtesy would be perfectly effective. It will teach those lessons especially powerfully, along with the equally important lesson of taking responsibility for mistakes and hurting others, if you have her with you when you apologize to this guy for your treatment of him (you can still ask him, nicely, not to sell to your child or approach her when she's alone). And that's another time when you don't JADE, by the way.