History

The first one is sort of hard to disprove because it's too vague. It may be that there are no records of such an event because it never happened, or because the records were destroyed or never written. It's one of those historically worthless unfalsifiable claims.

Like, the first thing you would want to know if you wanted to verify if this is actually true or not is what is this person's name? What lot of these stories tend to have in common is that the sources are unnamed and anonymous so you can't even look for them in documents.

The second claim is almost certainly bullshit. We actually have first hand accounts from some of the people who were closest to Stalin at the time. They would all have had to be lying for decades including long after "destalinization" when it was fashionable to slander Stalin.

The ones making these kinds of claims, mainly Trotskyites and revisionists from the Khruschev clique, were opponents of Stalin who were not directly involved in the initial meetings and could not have known except through other people, and those people never mentioned this.

Not to mention that the idea of Stalin threatening and accusing people is a very obvious attempt to evoke a Hitlerian image. That doesn't work because this is entirely out of character, by all accounts he had a very different personality to what the propaganda portraying him as this ruthless, paranoid dictator would have you believe.

If you listen to recordings of his speeches, or read the accounts of people who had conversations with him or interviewed him, they all portray him as remarkably soft spoken and intellectual. Which should come as no surprise because he was a huge nerd, he spent a lot of his time when he was not engaged in politics, reading and writing books.