No, it's not mixed. It's related to the saying about the people who get rich off a gold rush being the ones who sell shovels. In the buggy-whip case, it's about a company not understanding the market changing entirely to make them obsolete. The transportation market moved to cars, and so nobody needs a buggy whip.
The original reference is probably Levitt's "Marketing Myopia" (https://books.google.com/books?id=Zn4foOUm3AoC). Levitt uses it to illustrate that companies should focus on customers rather than products.
Note the imprint, "Harvard business review classics." What I linked to is a 2008 republication of a book from 1975. The buggy-whip analogy also appears in a journal article of the same name by the same author in 1960. More info here: https://hbr.org/2016/08/a-refresher-on-marketing-myopia
