I believe this is referring to the sound of these words out of the mouth of a southerner. For example, have a southerner attempt to talk about kudzu to a group

I believe this is referring to the sound of these words out of the mouth of a southerner. For example, have a southerner attempt to talk about kudzu to a group in Japan and they’ll have no idea what he is saying (I know this from first hand experience). Same with these other words—the vowels change and slide and are inscrutable (hard to understand) to those whom the words are native.