A more logical response is that the author did not know that the Earth was a sphere. The educated population generally knew that the Earth was at least roughly spherical in shape, but that does not mean that everyone knew that. I do believe that Muhammad was supposed to be rather uneducated. This would seem to support that belief.
There are several references in the Quran that suggest a flat earth (eg, "Allah spread out the earth like a carpet"), as well as a geocentric system (night and day caused by the sun and moon "in their orbits").
Although Islamic claims that Muhammad was an illiterate shepherd are somewhat dubious given the context (eg. his privileged upbringing and his successful career running Mecca's largest trading empire), it is entirely reasonable to think that his knowledge of established "science" was limited.
However, there are occasional nuggets, like the description of human embryology that closely matches that described earlier by Galen. One of Muhammad's companions, Ibn Kalada, was a physician who had studied at the "university" at Gundeshapur in Persia, where Galenic medicine was taught. This perfectly explains the passages that contain a rudimentary description of human embryology that some apologists hold up as an example of a "scientific miracle" in the Quran ("how could an illiterate shepherd have known about it?!").
Another classic "Quran scientific miracle" is the sex of worker bees (female). There is a passage in the Quran that refers to bees and although it never mentions their gender, there is a linguistic marker that is in the feminine. Apologists insist this means that it is stating that the worker bees are female "something only recently discovered by science!"
Had they taken the time to do a little research, they would have known that in his "History of Animals" Aristotle states that worker bees are female.
My favourite (you may have gathered by now that this is a pet subject of mine) is the "round earth miracle".
This is based on verse 79:30 -
"And after that He spread the earth." (which ties in nicely with the flat earth issue).
In Arabic, the word used in the Quran for "spread" has a root that can refer to the way an ostrich clears a patch of ground of stones to lay its egg. This has been interpreted to mean that it is describing a round earth, "like an ostrich egg" (yes, I know, but they are genuinely serious!). "The round earth was only recently discovered by science!!" (which seems to be the mantra of the scientific miracleist).
Had they done a little research they would have known that not only did Eratosthenes work out that the world was round 1000 years before the Quran was written, he actually calculated its circumference reasonably accurately.
Not only that, the "egg" description is the wrong shape. The earth is an oblate spheroid while an egg is a prolate spheroid. A better description (had it actually been describing it at all) would have been an apple or pomegranate.
Sorry to digress!