The sound comes from PewDiePie, whose And that's a fact delivery became a classroom meme for jokingly stamping an obvious statement as proven. Shared widely as a short button sound, it spread through reaction videos and student humour because it needs no setup: hear the line and the joke is already understood. It is still used today for the same reason, as a quick sarcastic closer that works alongside other punchline sounds like a correct ding or a badum tss after a statement lands.