I really don't know enough about horary to have a strong opinion on it, but the way I see the "job" is in the same way you would "employ" a doctor, tutor, landscaper, etc. You pay someone for his service. I would be providing writing services to the publisher and would only be under obligation for one particular assignment at a time. It would be up to the publisher whether he wanted my services again or not. Neither of us would have an obligation to the other after a project is finished. I would do the work at home, using my own equipment. I would not be going to the publisher's premises.
I'm adding all this not to belabor the question, but to try to learn more about how to read the chart.
I have not heard back from them, but it's only been a couple of days since I sent my resume.