The article is poorly written, which is not surprising given the quality of government education.
A coracle is not necessarily round:
http://www.bing.com/images/search?q=Coracles&FORM=HDRSC2
I suspect your top image is the closest one to the actual Ark seen from above. How about the fact that it’s black all round? That blew my mind. I’d always believed those drawings, etc. They’re totally off on that score.
The ratio of the ark of length to width is 6:1. So it had to have had a rectangular shape. However, I see your point on the shape you envision and agree the article is either very poorly written or misleading. I have seen several of these article on the web, and none of them even mention the description in Genesis. The comments from people are shocking. Most of them don't even know that we know what the approximately length of cubit is/was.
Good link on the Hebrew - I must learn more about that.