Often people want to post something about the situation at their job, and they're afraid to do so with their regular account. Such comments contain real information based on inside knowledge, the kind that HN readers love to get access to. That's the opposite of rumors. Indeed those comments frequently contain more and better information than would ever appear under the regular account.

It's also true that such comments can be counterfeited, which is where this gets complicated. But HN would be worse off without that class of comments. It's a legit use for throwaway accounts.

Are they verifiable? I don't think that's the best standard to apply to internet comments. The vast majority aren't. You have to assess credibility, but I wouldn't call that verification. In the case of a throwaway account, the only public information for assessing credibility is the content of the comments themselves, but that's not all that different from the usual situation on the internet. Admins have it a bit easier because there is other data we can also look at.