Concisely put, someone who has a deep knowledge of something gains, as a result, the capacity to appropriately hide its complexity through simple metaphor.

When someone doesn't understand as well, he or she cannot as easily extrapolate a simple metaphor, and can only give a technical answer.

When someone doesn't understand at all, he or she might simply hide behind impressive-sounding words.

This is largely because the knowledgeable individual is much more confident about leaving out technical details, because he or she knows which details are unimportant for a given context. The less-knowledgeable has not not yet developed a feel for which technical details are really important in understanding a given concept.

So, while an explanation filled with technical detail doesn't automatically mean the speaker/author is not knowledgeable, it does tend to work out that way.