Do you think the issue was something else? "People randomly see other people's content" is an issue that would immediately make me think some issue with caching is the culprit.

Given their openness in the rest of the communications, I don't see why they would make this part up.

Edit: Of course, I'm also curious what the actual bug was. A discussion below is suggesting several plausible ways (e.g. concurrency issues, insufficient entropy in some key) how a problem could happen under load (although many of these would also lead to the problem happening with less load, just much less often).