Replying again to say that I am extremely touched by both donations that I received, and I have sent them on to the address being used to gather funds by the bitcoin community as an apology to Dorian Nakamoto.
The other answers to your question are technically all feasible, but are all extremely unlikely to be how this was actually done.
This is just what third party cookies are. Cookies set from the server-side (ie, the Set-Cookie header) can set whatever domain they want -- and if that cookie happens to not match the domain of the page you're on, that's what's called a third party cookie.
Some browsers (primarily Safari IIRC), however, will automatically reject those cookies, either in all instances or depending on if you've interacted with that domain before.
Thank you, and I appreciate learning. But I think I'm reading something else on wikipedia. The article there says you can only set cookies on "the top domain and its subdomains"  and that third party cookies are those set by page assets (like images within a page) that are served from a different domain. 
My point was that it doesn't need to require much complexity at all; just an HTTP request served by the domain in question that passes along the cookies that need to be served from the new domain.
That's not the issue here. The issue is that Hacker News is on HTTPS, but the link he posted to dictionarydomains.co isn't. Browsers don't pass a referrer on links between HTTPS->HTTP. So, visits from HN don't have a referrer. Custom Channel Groupings won't help in this case, because GA is completely blind to what visits are referrer-blocked HTTPS
I've seen people bypass this by either:
1. Having a HN specific URL (sometimes just ?hn attached to the URL)
2. Just having HTTPS landing pages.
One thing that could help fix this behavior (on newer browsers) would be for HN to explicitly authorize passing the referrer using `<meta name="referrer" content="always">` or "origin"
I tried it out with a $20 card this morning (I've had it for 3 years and never remember to use it on the rare occasion that I'm at Starbucks). I just received my 0.014916 bitcoin via Coinbase. It took 2 hours between when I submitted it and when I received the bitcoin.