Not a mixed metaphor, it’s a standard phrase.

Note buggy WHIP makers, not buggy makers.

It is mixed because it is comparing two different class of items

whips to cars does not really compare. Cars to buggies would compare or perhaps whips to steering wheels.

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.

Watch the movie “other people’s money” for the original reference

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.

Well OPM came out in 1991 so I doubt it.

https://youtu.be/62kxPyNZF3Q

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

Thanks for the detail and I should have dug deeper

Because they invested in the new up and coming thing and transferred the knowledge that applied.