I think you have a point, but the difference is that a reactive dog behaves in an extreme, unusual, or unexpected way to new stimuli. It is expected for a puppy to be unsure of or frightened by new things, because they're babies. Kyleigh's reaction to the shovel was probably well within normal puppy behavior (just throwing the "probably" in since I don't know you
). But if she'd kept growling at it for 3 hours, or reacted every time she saw it afterwards, or whatever, then I would call her a reactive puppy.
To use another example, I have two dogs of similar age and breeding, one who I would say is reactive to strangers, the other isn't. They both react to strangers, and even the friendly one is standoffish (to my eye) until he gets to know someone. But he is still friendly and relaxed in virtually any circumstance. The reactive one may snap or growl at even a very friendly stranger. So both react, both are cautious, but only one is reactive.
I also don't think "reactive" hinges on past behavior. An experienced handler can prevent a bad situation from ever occurring with a dog who is naturally reactive (due to genetics, for example), but that doesn't mean the dog is any less reactive. It's a description of temperament and response to stimuli, not the dog's history. As a real-life example of that, my very reactive dog has never snapped or growled at anyone since I've owned him. I know he did with previous owners (part of why I have him), but if I didn't know that, I would still label him as reactive because when he's uncomfortable, his body language and behavior clearly tells that something bad will happen if he's pushed further. I choose not to let it get to that level, but he's still reactive. His history isn't important, it's his reaction to current stressors that matters.
To tread on maybe controversial waters, I think it's kind of like mental illness in people. Everyone gets sad sometimes, but when it interferes with your daily life and there's no real reason for it, then you probably suffer from clinical depression. Most people daydream, but when those daydreams take over to the point you can't tell reality from fantasy, you probably have a delusional disorder. Similarly, most dogs will react to things they think might be dangerous (and puppies will react to more, because they know less), but when those reactions are beyond the normal range and interfere with socialization or training, then you probably have a reactive dog.