The posted article is by 3blue1brown (Grant Sanderson) himself. Where the article says "Early in 2019, I published a set of three videos about Galperin’s result..." the link is to the playlist https://www.youtube.com/playlist?list=PLZHQObOWTQDMalCO_AXOC... of which the video you posted is the second video. IMO, it's best to watch all three (or at least the first two) together :-)