HN has value larger than for just for the community of people commenting here. It is also used as a platform for YC companies. YC Founders can even see each others usernames in orange color[1].
A spamming actor could also be testing the limits of the system now for a future attack. Anyway, this is the job an Infosec team usually deals with. Hopefully @dang / HN team has access to people with such skillset.