Did you notice that the article asks the question "when does human life begin"? Human life, human organism, and human being end up being treated as one and the same, and (from memory) at one point she says "human organism i.e. human being" before she's even made her argument. Although any organism can certainly be a "being" in some senses of the word, so can anything that exists (including human eggs and sperm). But when the phrase "human being" is used, it's usually understood to mean a person.
Yes I did notice the terms being used as if they were synonymous and as you say she did state "human organism i.e. human being" in her summary, which she placed at the beginning before any arguments. As I said I would describe a human being as an organism based on the definition she chose to use, I just had a problem with her trying to draw parallels between the tissues and organs of a developed human, and the chemical reactions of those initial precursor cells.
Of course I say this, but I do work in a microbiology lab where I regularly refer to bacteria as organisms. However these single-celled organisms have reached the highest level of complexity they are going to attain, whereas a zygote is still on the first step of a long journey to the level of complexity we would refer to as a human being.
Religious "pro-life" groups are remarkably fond of phrasing the question "when does an individual human person begin" as "when does human life begin"? Why?
I'm really not sure, but I suppose it's easy to point to that first diploid cell with human DNA and say there is something that fills the basic criteria for life and it's human. It also lends well to this tendency to describe every point in development as a 'baby' which is certainly emotive language.
It makes me think of that old 17th century idea of the homunculus i.e. the zygote, or even before, is a fully formed human, gestation just allows it to grow bigger. Some of this rhetoric can be seen in the article with the idea of the zygote working towards developing a complete human body. Also the analogy of the car manufacturing with the embryo differing because it constructs itself without outside help, which is wrong since it is working to the 'instruction set' obtained from the sperm and egg of it's parents.