Actually, Arnold was only drawing from Proclus Diadochus, who wrote the following in his Commentary of Euclid's Elements (Book 1):
We must next speak of the origin of geometry in the present world
cycle. For, as the remarkable Aristotle tells us, the same ideas have
repeatedly come to men at various periods of the universe. It is not,
he goes on to say, in our time or in the time of those known to us
that the sciences have first arisen, but they have appeared and again
disappeared, and will continue to appear and to disappear, in various
cycles, of which the number both past and future is countless. But
since we must speak of the origin of the arts and sciences with
reference to the present world cycle, it was, we say, among the
Egyptians that geometry is generally held to have been discovered. It
owed its discovery to the practice of land measurement. For the
Egyptians had to perform such measurements because the overflow of the
Nile would cause the boundary of each person's land to disappear.
Furthermore, it should occasion no surprise that the discovery both of
this science and of the other sciences proceeded from utility, since
everything that is in the process of becoming advances from the
imperfect to the perfect. The progress, then, from sense perception to
reason and from reason to understanding is a natural one. And so, just
as the accurate knowledge of numbers originated with the Phoenicians
through their commerce and their business transactions, so geometry
was discovered by the Egyptians for the reason we have indicated.
...
After these Pythagoras changed the study of geometry, giving it the
form of a liberal discipline, seeking its first principles in ultimate
ideas, and investigating its theorems abstractly and in a purely
intellectual way. It was he who discovered the subject of proportions
and the construction of the cosmic figures.
Source: https://mathshistory.st-andrews.ac.uk/Extras/Proclus_history_geometry/