I had upset the peasantry by, er, murdering quite a lot of them. To be fair, they were about to hang a deserter. To make things right I agreed to help with their protest against taxation, which is why they asked me to kill a barghest for its blood: "The green really pops on our protest signs." But I hadn't got to grips with the combat system yet and the barghest ended up collecting my blood instead, which is how Dandelion got yet another story of Geralt's many deaths to turn into a ballad.
Remember Reigns? Nerial's game of Tinder-esque swipe-based monarchical decisionmaking was massive in 2016, followed by a sequel called Reigns: Her Majesty and spin-offs in other settings. Reigns: Game of Thrones seemed like a particularly perfect fit with its stories of bastardry and beheadings.