I’ve taught my DC that “stranger danger” can be a bit of a myth, as people who are dangerous to children can be anywhere and could actually be a smiling sports coach who everybody loves, a school teacher, a relative, a family friend…
I have taught them that the majority of people are good and kind and helpful and safe to be around. But the point is that we cannot tell how trustworthy someone is by looking at them, or even based on the job that they have, or based on other people’s opinions. When they were younger they understood that someone is a safe person to talk to in some settings (sports coach at sports practice for example, school caretaker while in school) but if they are approached by that person in another setting, they actually fall back into a stranger category at that point in terms of trust.
We have worked on “gut instinct” from being quite young, on the “it’s more important to be safe than it is to be polite” rule and on keeping really open communication with each other at home.
My DC aren’t paranoid wrecks, they honestly aren’t, they are happy and confident and friendly.
There is no point sugar coating things in terms of “innocence” though. There are sex offenders everywhere who will happily train for years to get into close contact with children, as well as your opportunist “man in a mac” types.
Re: would a DC break rules by running off during a dangerous incident… I think that comes the under “gut instinct/better to be safe than to be polite” headings. In the same way, I don’t encourage blind obedience, it is always okay to say no to an adult when asked to do something you think is wrong (and that is a very important thing for an autistic DC especially OP).