If no one was allowed to attend, how do you get such good scoop?
I'm pretty sure I carefully preceded my assessment with the phrase, I believe. That should have negated your question. I do leave "scoops" to the "news" media. Perhaps what you meant to ask was how I arrived at my conclusion. It was a mixture of both deductive and inductive logic but mostly trustworthy inductive logic. Hillary Clinton was not a guaranteed loss at that time for the Democratic nomination but her chances were slipping away. Barrack Obama did not select Hillary Clinton as his vice presidential running mate although that would have been a powerful ticket pairing an electable black candidate with a female running mate. Hillary was subsequently named as Mr. Obama's Secretary of State. That position provides no real power or wealth but it does serve as a meaningful positioning for a future presidential candidate.
Perhaps your speculations will be more accurate than my own. I doubt it. Maybe when we get a chance one of us will take the opportunity to query Mr. Clinton or Mr. Obama as to what took place in that discussion. Of course, that would dictate the questioner would need to be comfortable with accepting a good chance of truth in the response.
AS to czuch's assessment, I tend to agree. Joe Biden was and has been Barrack Obama's most effective anti-assassination insurance.