It's an in-joke. The monkey, named Suzzane, is the mascot of the Blender Foundation. When creating something technically complex, like a physics simulation or a shader, it's handy to have something more complex than a sphere or a cube to use as a test object.
不過看影片發現自己的3D能力大概就是跟1980年代的人差不多
BLENDER的猴子之謎也解決了，以前有疑惑過但沒查過為什麼XDDD