I'm not GURPS, but the video that he posted is for a game called Plague Inc. It's a game on PC and mobile devices where you create your own virus, and your goal is to exterminate all of humanity before scientists create a cure for your disease. To have the best chances of infecting everyone, you must mutate symptoms and forms of transmission (including immunity to colder countries, and planes/ships).
In the game, there are different scenarios you can play through, such as the Fake News one that GURPS has posted the video for, although I am personally unfamiliar with it myself. To put things in a different perspective, it's more or less similar to the COVID-19 outbreak we are dealing with now, in the terms of it spreading rapidly, people dying, and scientists struggling to create a vaccine to keep potential infections at bay for as long as possible.