The sound comes from Team Fortress 2, Valve's class-based multiplayer shooter released in 2007. Players know it as the audio cue tied to critical hits, especially random crit moments that can swing a fight instantly. Because TF2 remained heavily played and widely clipped for years, the sound spread into montages, meme edits and other game communities. It is still used because the cue is so short and readable: even outside TF2, people immediately understand it as a sign of huge damage or an absurdly strong hit.