May I ask what kind of material this table is made of?

This is willow wood.

Willow bark dark gray-black, skin grooves wider, heartwood reddish, sapwood dark white, clear annual rings. Wood structure is fine and dense, soft, smooth after planing, flammable, slightly poorer corrosion resistance. White wood width with the growth conditions and transformation, the color is light beige-brown. Its heartwood color just the opposite, for light reddish brown to brownish gray.

Willow wood has a fine and uniform grain, although usually straight grain, sometimes there will be diagonal cross wood grain, or show round grain. Folk have used willow to make furniture.