Note that it has nothing to do with assuming the worst. It's all about potential. For an extreme example, imagine a stranger almost fell off a bridge, and you're pulling them up. If you let go, they will fall to their death.

Is this an appropriate moment to ask them out on a date?

It's obvious to me that the answer is "no." You literally hold the power of life and death over this person. They have no idea what your intentions are. You've put them in a really tough spot and it's completely inappropriate.

Now, this has nothing do with assuming that you'd actually drop this person to their death if they rejected you. It's merely that there is the possibility. You might. Even if the odds are a million to one, put yourself in that person's shoes: would you take that risk? This is a total stranger. You don't know what they're like. It's possible they're a nutcase who freaks out whenever they're rejected. (I'm sure you've met people who do this.) Chances are good that they're a completely normal person... except, of course, that a normal person wouldn't be asking the question in the first place.

Now, the actual interview thing obviously is not on the same scale. There's no life-or-death situation (probably... stalking ending in murder is a real thing, and this guy knows where she lives) and it's fairly safe to say "no." But the potential is still there. We're not assuming the worst, merely acknowledging that the worst is possible, and that alone is enough.