The thing is, I tend to think about the sorts of things which are complex enough that you can't trivially describe them in a linear format. Imagine that somebody asked you to tell them about programming. Programming is such a huge and complex topic that there really isn't an effective way to begin explaining it without putting significant forethought into how to explain it, even if you're an expert programmer. So, unless you've put thought into how to explain and teach it, if someone randomly asks you, you're probably going to fumble and be verbose. (This is one of the reasons many professors are bad at teaching.)

Of course, in the context of the article, somebody interviewing with investors probably should have thought out in advance about the sorts of things the investors would want to know and ask about, so they shouldn't be fumbling too much.