What is the size of the object in the jellyfish video

When rewatching the video it appears that the object is actually quite small relative to the background. When looking at the linked image it’s nearly equal to the size of the fence post in the background, which leads me to believe it can’t be more than a foot or two tall. Since the object is higher up and closer to the camera then we would expect its size to appear larger than it actually is. Do I have this all wrong? What do you think about the size?