If they were motivated enough by this story to delete 20 years worth of history maybe they were motivated enough to create an account and talk about it?

They could just be very concerned with privacy.

One of the best things about hn is that accounts are cheap and disposable. For me, most threads get their own account. I don't like people tracking my full comment history across the internet with it all tied to one account, even when it's just one I use to comment on harmless tech stories