If you try scrolling down, you'll note you can actually read the article. LWN lets subscribers share (temporary) paywalled articles with anyone they like, even on public forums like HN. They are nice like that.
Links to LWN subscriber content appear on HN from time to time - not too often, and I would guess they do more good than harm to them.
> Where is it appropriate to post a subscriber link?
> Almost anywhere. Private mail, messages to project mailing lists, and blog entries are all appropriate. As long as people do not use subscriber links as a way to defeat our attempts to gain subscribers, we are happy to see them shared.