Well, he was wrong. I've never heard of not putting in rebar in a slap that big. There is nothing to hold the concrete together. Plan on those cracks getting worse and worse. I am not in the industry, but have had many things poured, as well as helped out on many jobs. From Driveways to walkways I've never seen a job not have at least wire mesh.
I'm sure I'll get blasted by someone who knows more who would say you didn't need it, but I never would have let them pour without putting some kind of metal structure inside there. I know when I did my patio a few years ago with friends, it was in the code that it had to have the wire mesh. And it was about 2/3 the size of your pour. (I'm in Illinois) It even had to be inspected and in place before I poured.
Basically it needs to be redone with mesh or equivalent. He did a half *** job.