I was also ready to chalk this up to "Yet another security researcher needs to learn how to play well with others..." but the moronic and indigent response from "Sean" makes it clear who's wrong here.

Imagine an alternate universe where "Sean" wasn't so aggressively stupid, and instead replied: "Thanks, JayeLTee, we took the database down while we do an audit. We don't think there were any access, and we would rather you not go public about the findings, but it will take us time to check. Please hold off on your publication until [DATE] and we will be in touch."

There. That didn't take much effort! But, no, "Sean" chose belligerence and threats rather than professionalism. I don't know what is wrong with people who just seem to default to "bad attitude" in their communications.