They may be the only meteor shower caused by an asteroid. Plus most well known meteor showers, like the Perseids and Leonids, are very old. Not the Geminids. The first Geminid shower suddenly appeared in 1862. Astronomers immediately began looking for a comet.
Most meteor showers result from debris that that boils off a comet when it passes close to the sun.
When Earth passes through the debris, the result is a meteor shower. It wasn't until 1983, that NASA discovered a curious object moving in the Geminid orbit, but to the surprise of many it wasn't a comet. The source of the Geminids was apparently a rocky asteroid named 3200 Phaethon. Many astronomers now believe that Phaethon is an extinct comet with a thick coat of dust. So it looks like an asteroid, but underneath lies the heart of a comet.