Winky, can I just add, without trying to sound too up myself, that I've seen you have posted this in AIBU too. There you have got a more balanced view insofar as you have got people who aren't as nuts about dogs as me... but you have also got people who aren't as experienced with them too.
You've also got the odd "string 'em up and kill 'em" brigade type, which does nothing for my patience levels and blood pressure!
Trying to get a bit of perspective here, there will always be a monority of dogs which are a danger to something, be that children, men, cats, whatever. Similarly there are people out there who are bad owners and humans who are a danger to other humans and/or animals.
The majority though, are reasonable and decent, be they dogs or human beings. In your situation, we just don't know.
Can I play devil's advocate and put another spin on it?
The owner comes out of the shop not having seen the incident. He doesn't know what your DD has done but knows that his dog has never before caused a problem. Maybe even he has children of his own who live peacefully with his dog. Although his dog reacted in fear of your DD/excitement and caught her accidentally/was in pain/feeling off-colour he feels that your DD must have shocked and scared his hitherto friendly dog to provoke such a reaction.
He therefore doesn't consider his dog a bad animal but remonstrates with you for allowing your DD to approach his dog and frighten/distress him and for permitting DD to get close to his dog without permission as he knows this to be out of character for his dog.
He is also painfully, fearfully aware of the ambiguous terms of the Dangerous Dogs Act, which could see his beloved friendly family pet killed before a trial, by what is proven to be a kangaroo court, without sufficient evidence or recourse to justice. He therefore reacts with an instant and instinctive desire to protect his dog.
That doesn't make him wrong or a bad owner. On the contrary, IF he reacted because he feared the things I've described and had no prior reason to be concerned about his dog, he is a good owner.
As I said, we none of us know.