I don't see how any of the words in the quote have anything to do with oaths and swearing -- words which to me are akin to "promise".

It makes more sense (imho) to think of "expletive" in its original (i.e. what I would consider its more proper) sense -- namely, filler.
Now, people (pretending to be grammarians) have come to equate "words which were inserted unnecessarily" with "words which should be stricken out".
And hence, any word you think shouldn't be there is now being called an expletive, even if your reasoning has nothing to do with superfluousness.
A better example of expletive, in this stricter/more proper sense, might be:

You know b....y well what a f.....g expletive is!

But in the quote, the fifth word is not filler. Rather, it is simply a vulgarity. It's not even obscene, let alone profane.

Now, the last word of the quote is a different matter, and y'all have already hashed that one quite to death.