It seems like an unusual rephrasing of the saying "reasonable on the face", which means "reasonable upon first appearance, without considering deeper aspects."

It's judging a book by it's cover.

My understanding (not the author): "prima facie" is a legal term for "on its face", and this is saying the same thing but phrased in a different way. It looks reasonable on its face, due to being "superficially similar" (author's words). But when you look a bit deeper, it is not.