The terminology is getting really confusing, to me anyway.
You just have to remember that in a silver halide process (most photography of yore), light causes darkness on the target medium.
So when you shine light through an original, what is light in the original causes darkness in the target.
Therefore making a true copy of either a negative or a positive slide requires two of these inversion steps to restore the original parity.
For reference, I'm no fan of the wikipedia wording you quoted. I learnt by doing at a very amateurish level, and didn't grow up with the formal terminology, and their description doesn't correspond to what I did and saw. The "inter-" denotation in general us useful though, it tells you it's the half-way inverted step of a duplication process.
(Ug, I might confuse matters if I add that the inter itself isn't intrinsically an interpositive or an internegative, as it doesn't know what it's the inverse of, it just carries lightness where there was darkness and darkness where there was lightness. Ooops, too late.)