It is even worse than that! Who was this Eratosthenes? Did he even exist and if he did, did he actually do and say all the things attributed to him?
Ancient history is full of 2nd, 3rd, 4th etc. hand accounts of what someone said or did but the original is very often conveniently lost to posterity.
"Eratosthenes' method to calculate the Earth's circumference has been lost; what has been preserved is the simplified version described by Cleomedes to popularise the discovery.[14]"
https://en.wikipedia.org/wiki/Eratosthenes