GitHub is explicitly listed as "social media" on the optional question that is on the ESTA [1] form since 2016. If I remember correctly, the wording is relatively broad, so I would guess that HN and Reddit count as well.
Just an FYI - that website (evisaonline) isn’t an official government site. They seem to be some third party who provide some sort of ESTA application service. The official site is at https://esta.cbp.dhs.gov/esta/
[1] https://www.evisaonline.com/en/usa/esta.html