This is an extremely silly observation for HN, given that the usernames are published openly with every comment. My username is quite obviously "throwaway09223.

This is an extremely silly observation for HN, given that the usernames are published openly with every comment. My username is quite obviously "throwaway09223." There's no need to enumerate anything. Avoiding username enumeration is a reasonable goal for some sites in terms of hiding PII, but it is very obviously not a necessary security measure.