Hmm, I´d say NOT possible. I only played until 10AD in that GOTM, no more time, but my plan was similar, early conquest. I researched directly to the Great Lighthouse, only 3 or 4 settlers left my capitol before starting the project. Yet, it was completed almost 1000years later. While his cities still where churning out settlers at an enormous rate.
Ok, let´s do some simple calculation:
Thebes has excess food of 3 under despotism, no matter any irrigation. This means it needs 7 turns to grow. So, it can produce a settler after a minimum of 14 turns. Would be 700years. So, 3300BC.
Let´s assume the first 2 cities being settlers from huts (Memphis, Heliopolis). Then Elephantine would be the first that can be produced by a "real" settler. The next settler from Thebes can then be produced only much later.
The other 2 cities have excess of 2 food, needing 10 turns to grow =20 for a settler. So, they can produce a settler earliest after 1000 years after founding.
But after Elephantine, 4 cities are made within 5 turns. Ok, let´s assume all huts on the continent (5 IIRC) give a settler, which is almost impossible.
Now all hut settlers are used, we look at the next time interval, the next 7 turns. We are now 28 turns after start,
Until that time Thebes can produce a max of 2 settlers (14 turns to reach size 3). The other 2 earliest founded cities can produce only 1 each. So we have a max of 5 settlers, founding 6!!! cities in that time. Let´s assume further, the initial worker is added to another city, we have 3 more to choose from. Then we get the sixth worker, although I doubt that´s possible.
Now, only 2 cities, the last 2 founded earlier, are capable of producing a settler during the NEXT 5 turns, where 3!!! cities are founded. Now we have no possibility of achieving that, at least IMO.

Now, these calculations did not take into account that Thebes can´t reach the 3 food tile until 10 turns later!!!
And not too mention that it´s IMPOSSIBLE to reach 2 huts with the worker until 3500BC.
Now, this only took into account the food needed.
He also researched a lot during that time, build military units to explore and even accumulated the shields needed for a Great Wonder.
I say it´s
impossible. Especially when looking at how the game develops further. A good way to achieve such a growth rate is to let a settler only take away ONE pop point.
But I also say, let´s wait and hope for a reply from the player in question. And to take a look at earlier achievements. His early finishes are spectacular and he won several awards with them. So there should be a closer investigation.
