Sometimes I find an outsider in a conversation with little or no knowledge about the subject or ground already covered in the conversation makes a random guess about a question no one can answer and it turns out to be correct. I have experienced this often enough that it seems like there might be a word or phrase for it, but if there is I don't remember it. Any insight would be appreciated!
Example:
Wow, Bert only said that it might be catalytic converter because he heard us say that term earlier in the conversation. He doesn't know anything about cars. I can't believe he was actually right! That was a real ________!