The Bible insists that Noah's flood was global and no one survived except the believers who boarded the Ark with Noah. However the Quran says that the flood was local and all nations other than Noah's survived.
Local floods are very common however there is no scientific evidence for a global flood. But stories of a global flood are found in many ancient cultures all-around the globe. If it were a global flood, as portrayed in the Bible, no one would have survived other than the believers who boarded the Ark with Noah. There would have been no disbelievers who didn't board the Ark and survived. However the Quran says something else, it says that there were disbelievers who didn't board the Ark and still survived:
٤٨ قِيلَ يَا نُوحُ اهْبِطْ بِسَلَامٍ مِنَّا وَبَرَكَاتٍ عَلَيْكَ وَعَلَىٰ أُمَمٍ مِمَّنْ مَعَكَ ۚ وَأُمَمٌ سَنُمَتِّعُهُمْ ثُمَّ يَمَسُّهُمْ مِنَّا عَذَابٌ أَلِيمٌ
In the Quran other people survived. Since God will punish them later then definitely they were disbelievers who were not onboard the Ark. If only believers boarded the Ark but still disbelievers survived then this means that it was just a local flood. Those who were not in the area survived.
The very next verse says that this story was not known before:
٤٩ تِلْكَ مِنْ أَنْبَاءِ الْغَيْبِ نُوحِيهَا إِلَيْكَ ۖ مَا كُنْتَ تَعْلَمُهَا أَنْتَ وَلَا قَوْمُكَ مِنْ قَبْلِ هَٰذَا ۖ فَاصْبِرْ ۖ إِنَّ الْعَاقِبَةَ لِلْمُتَّقِينَ
The Bible insists on a global flood killing all disbelievers. The story in the Quran, that other disbelievers survived, was not known to previous cultures and the Quran was the first to proclaim it.
In the Quran the last prophet was sent to all nations however Noah was sent to just his own people:
Al-alameen الْعَالَمِينَ in Arabic means "all nations". The last prophet was sent to all nations. However Noah was not sent to all nations but sent to just his own people:
٥٩ لَقَدْ أَرْسَلْنَا نُوحًا إِلَىٰ قَوْمِهِ فَقَالَ يَا قَوْمِ اعْبُدُوا اللَّهَ مَا لَكُمْ مِنْ إِلَٰهٍ غَيْرُهُ إِنِّي أَخَافُ عَلَيْكُمْ عَذَابَ يَوْمٍ عَظِيمٍ
In the Quran Noah was sent to just his own people, not to all nations. And those who were drowned by the flood were disbelievers from his own people, not from all nations. The Quran never said that God drowned all nations Alameen الْعَالَمِينَ. However the Quran consistently said that God drowned only the people of Noah:
٣٧ وَقَوْمَ نُوحٍ لَمَّا كَذَّبُوا الرُّسُلَ أَغْرَقْنَاهُمْ وَجَعَلْنَاهُمْ لِلنَّاسِ آيَةً ۖ وَأَعْتَدْنَا لِلظَّالِمِينَ عَذَابًا أَلِيمًا
God drowned disbelievers from Noah's own people قَوْمَ نُوحٍ and made them a lesson for mankind. The Quran never said that God drowned mankind.
Noah was sent to just his own people, not to all nations. And Noah presented God's revelations to just his own people, not to all nations. And those who rejected the revelations were from Noah's own people, not all nations. So God drowned disbelievers from Noah's own people, not all nations. In the Quran all other nations had nothing to do with the flood. This means that it was just a local flood.
The Quran referred to the stuff Noah owned only:
٤٠ حَتَّىٰ إِذَا جَاءَ أَمْرُنَا وَفَارَ التَّنُّورُ قُلْنَا احْمِلْ فِيهَا مِنْ كُلٍّ زَوْجَيْنِ اثْنَيْنِ وَأَهْلَكَ إِلَّا مَنْ سَبَقَ عَلَيْهِ الْقَوْلُ وَمَنْ آمَنَ ۚ وَمَا آمَنَ مَعَهُ إِلَّا قَلِيلٌ
"Tannur التَّنُّورُ"is a whole in the ground for baking. When the "Tannur" fills with water; however it is in the singular mode not plural. If it were a global flood then every Tannur on Earth should have filled with water; but this wasn't the case, only the Tannur that he owned. From the "Tannur" we know that this verse is referring to what he owned only. Similarly in the same verse the animals that boarded the ark are also the animals that he owned only, not every animal on Earth.
There is no scientific evidence for a global flood, however local floods are very common.
How could an illiterate man who lived 1400 years ago have known that there was no global flood?
The Quran (Koran, the book of Islam) contains scientific knowledge that could not have been known 1400 years ago. It ranges from basic arithmetics to the most advanced topics in astrophysics. You are invited to go through those miracles and judge for yourself.