If someone is so concerned about sources, they can include it in the reply after the parent.
Nobody likes people who complain but won't do anything about it.
If the lack of citation bothers you so much, maybe you should include it yourself. Nobody else gives a shit in case you haven't noticed.
The original comment had no citation yet it received upvotes, contrary to your view of HN. Everyone is intimate with Google and they can follow the instructions in this thread to find the appropriate sources. If you want citation in the format you find in academic papers, that is on you, not the original commentator.
I can't help you any further but there are plenty of comments being posted as we speak that lack citations, you better get on that quick!