Considering that there is no mention of GDPR in the HN FAQ or on the "legal" page, my guess is that their position is that GDPR does not apply.
According to Article 3 of the GDPR, it applies to:
1. Processing that takes place in the context of processors and controllers that are in the Union, regardless of whether or not the processing itself takes place in the Union.
2. Processing the data of subjects who are in the Union by controllers or processors who are not in the Union if the processing is related to offering goods or services to such subjects in the Union or the processing is related to monitoring the behavior of such subjects that takes place in the Union.
I don't know how HN is structured, but I've not seen any indication that they are in the Union, so #1 probably does not apply.
#2 applies if they are doing processing related to "offering goods or services to such subjects in the Union" or "monitoring the behavior of such subjects that takes place in the Union".
One of the recitals elaborates on the first branch of that:
> In order to determine whether such a controller or processor is offering goods or services to data subjects who are in the Union, it should be ascertained whether it is apparent that the controller or processor envisages offering services to data subjects in one or more Member States in the Union. Whereas the mere accessibility of the controller’s, processor’s or an intermediary’s website in the Union, of an email address or of other contact details, or the use of a language generally used in the third country where the controller is established, is insufficient to ascertain such intention, factors such as the use of a language or a currency generally used in one or more Member States with the possibility of ordering goods and services in that other language, or the mentioning of customers or users who are in the Union, may make it apparent that the controller envisages offering goods or services to data subjects in the Union.
Does HN "envisage" offering services to people in the Union? Or are they a site that is merely accessible from the Union without envisaging offering services there?
There's a recital that elaborates on the second branch, too:
> In order to determine whether a processing activity can be considered to monitor the behaviour of data subjects, it should be ascertained whether natural persons are tracked on the internet including potential subsequent use of personal data processing techniques which consist of profiling a natural person, particularly in order to take decisions concerning her or him or for analysing or predicting her or his personal preferences, behaviours and attitudes.
Does the data HN stores about its users satisfy this? And if it does, is the behavior being monitored taking place in the Union?