It's real. I was totally surprised when that was the URL it picked.
So basically it failed at anaphora resolution.
Seen another way, you asked it for "the video" and so it gave you the video.
In vague cases, GPT-3 functions approximately as well as a markov chain - it will give you the most “probable” sequence of tokens. There’s some implementation details regarding how it deals with tokenization, but unless you really increase the randomness (“temperature”) you’re likely to get very popular YT video IDs.
In other cases, it will “hallucinate” things like URLs, UUIDs, hashes, and other things that are basically a random string of characters. In my experience it will make UUIDs that have the right number of characters but seem suspiciously non-random and don’t fit any of the defined UUID formats.
Fun stuff.
As predicted by Scott Adams in October 2001 ;)