> The people likely to talk to strangers unprompted are also likely to ignore those kind of messages.

No, that obviously false. They might be more likely, but they are certainly not likely.

I don’t think it’s false, much less obviously false. On one hand I have my personal experience about it, on the other you can see there’s only a small range in the “I want a conversation” scale where they want it enough to ignore the nonverbal signs that the person doesn’t want to talk but not enough to ignore the verbal ones.

Well, I don't see a "small range" at all. It's the opposite, extroverted pleople usually have better social skills than ones with social anxiety.