They're referring to the mythical animal, using a metaphor to express that such a company is mythical or non-existent. Coincidentally, this is same metaphor that the person who coined the term "unicorn company" was using.

Given that private companies with over $1B in revenue actually exist while examples of "[companies] that values programming and real productivity" are yet to be forthcoming, the parent post is using the metaphor correctly and the finance world is not.