[yummybear]

I don't believe this is compliant with the GDPR. Afaik usernames are considered personal data, as are user ids. Both are a form of online identifiers:

"Natural persons may be associated with online identifiers provided by their devices, applications, tools and protocols, such as internet protocol addresses, cookie identifiers or other identifiers such as radio frequency identification tags. This may leave traces which, in particular when combined with unique identifiers and other information received by the servers, may be used to create profiles of the natural persons and identify them."

[DanBC]

Sure, if I can identify the natural person from the name yummybear then yummybear is personal information.

But HN simply can't do that for most accounts, and so for most people their username isn't personal data.