Well, there you go. Even if you could see all the kingdoms of the world, you couldn't see their splendor: much of the splendor is kept indoors. So it must have been clairvoyance.
It still suggests he was taken upon a high mountain and was shown all the kingdoms of the world. If you're going to suggest that maybe he just imagined that he could see all the kingdoms of the world, then he wouldn't have needed to go upon a mountain to do so. Think about it from a flat-earth perspective from 2,000 years ago or more. If you believed in a flat earth, this passage would make complete sense.
So yeah. This verse does not count as Biblical evidence that the Earth is flat. Next?
Daniel 4:10-11
"These are the visions I saw while lying in my bed: I looked, and there before me stood a tree in the middle of the land. The tree grew large and strong and its top touched the sky; it was visible to the ends of the earth."
Also, remember the classic belief in a flat earth in which the continent of earth was surrounded by oceans on all sides and had a great ocean of water beneath the landmass as well. There was supposedly a solid dome at the edge of the ocean that went into the sky (and in fact held the sky in)... outside this "arena dome" was another enormous ocean of water. This can be understood through a reading of Genesis.
Genesis 7:11
"...on that day all the springs of the great deep burst forth, and the floodgates of the heavens were opened."
Genesis 1:6-8
"And God said, 'Let there be an expanse between the waters to separate water from water.' So God God made the expanse and separated the water under the expanse from the water above it. And it was so. God called the expanse 'sky.'..."
Genesis gives a pretty good picture into the flat earth beliefs of the Bible. Other than that, those other two passages about seeing the entire world or seeing something from the entire world.