Error 418 is an April fools prank specification that isn't actually useful anywhere and has only really been used as a long running joke in the specification. Despite this, it's still used for some reason as placeholders or of the sorts.
Some interesting things to note about the site is that it actually returns a
503, which means nginx is setup to respond with the 418 page for some reason. I imagine it's for as I said, a placeholder.
WhoIs for kiwifarms.net also shows a change, instead being linked to epik.com nameservers.
I imagine null finally transferred the domain to another service.