Never assume that a dog approaching something or someone means that they are comfortable with it. Indeed, it can be quite the reverse and if the person responds, that is exactly what could cause the dog to panic.
This recent article from Denise Fenzi really hit home for me because it describes Ava to a T. Often she is very cautious about new things but, being a terrier and a curious being, she is always willing to explore those things. There’s a caveat to that, though: she must control the exploration process. Forcing her to interact with someone or something is guaranteed to put her over threshold and into a reactive state. It would be as if someone forced you to interact with the very thing you’re slightly afraid of. You want to learn more about it but at your pace!
Ava is super sensitive and very cautious, so when she meets new people I ask them to completely ignore her. They are the spider that she is curious but a little nervous about, and if they engage with her (i.e. the spider moves) it triggers her fight/flight response. Does that mean there’s something wrong with Ava? Nope. She’s an individual. Do people have a hard time wrapping their heads around this? Oh yes, they do! They expect all dogs to like people on sight, which is a flawed cultural expectation that Americans have (I’ve noticed it’s not that way in some other countries, like Japan).
Bottom line: be sensitive to your dog and treat them like an individual!