I'm sorry, but you've been misinformed. I spent about a decade studying hair structure and chemistry - and the horse hair in the electron-microscope photographs that I posted a link to looks exactly like many examples of human hair.
I don't know what your definition of a "barbed scale" is - but a platelet and a scale are synonymous concepts, and hair has them. The accepted term in North America is 'cuticle'. They are not uniformly shaped, or rounded like a fish scale as is sometimes shown in simplified diagrams, but the edges do lift under application of heat or alkaline substances. The opposite is also true - the cuticle will seal up if shocked with cold water or exposed to a mild acid. If you've seen a photograph of the hair shaft in this state, you will have seen that it looks nearly perfectly smooth - surface irregularities aside. Remember that the cuticle itself is only a few microns thin, and translucent and would be difficult to see when closed down.
It *is* directional. That is apparent in the photos. Now whether most bow hair has been kept in the original orientation until it is installed on a bow, or if the hair strands themselves have a "random orientation" because of handling - that I do not know. A couple of people have posted that the hair is kept tied together and oriented as it came off the horse - and that seems reasonable to me.
Whether you need to rosin your bow in one direction is obviously up to you and your teacher.
