Dogs do tend to bark at other dogs, however the JRT was just doing what most terriers do. It doesn’t mean that it’s a “mean dog”. Terriers protect their territory and pack members above all else.

The owner was doing the responsible thing, she had her dog on leash. I personally would have reported you the first time. One of the things that makes me the angriest is when I’m out walking my dogs and encounter someone whose dogs aren’t on leash. Many people think they know their dogs well enough to walk then without a leash, but you yourself say that your dog hasn’t ever reacted that way before. Sometimes our dogs will react differently to other dogs and are therefore unpredictable and shouldn’t be off leash in a public area, unless designated as off leash. Period. This goes for anyone’s dogs. IMHO