It's not only that, it's a cooking technique. You literally smash and press the patty onto a high-heat cooking surface (grill, iron cast skillet, griddle, etc) for a short time, and the combination of high heat and pressure results in a larger surface area for the Maillard reaction - the thin smashed patty caramelizes fast, locking in the juices in the meat but creating crispy, browned edges and surface. My favourites are Oklahoma smash burgers where you add onions and smash the meat into it, caramelizing both.