In (Arabic) Tafsir (e.g. Qurtubi), you will find both what I said and what Charles said. So there are two interpretations for this verse, one of them is that it was a reference to a geographical place. (a hot spring in the West). The other one is that the sun was sinking in a hot spring. (I just checked the Tafsir by the way).
If I were God, and I am not, I'd know that this would be a matter of dispute in the future and I'd have said "He reached a place by a hot spring just as the Sun disappeared behind the horizon". Factually accurate, indisputable, and not going to confuse the flat-Earthers of the time.
Sure Zakir Naik would be out of a job, but that alone would be worth it
It's funny though how God with omnipotence isn't as careful as I am with hindsight and 1400+ years of technological advancement.....isn't it?