Interesting...
I didn't check the graphs, but I trust you that they indeed settled on T1.
So let's see :
- Polytheism is 156/1.2 = 130 beakers
- Until T11, there is no worker, no pop growth (as indicated by their score), so the beakers come only from : 1 free beaker + 8C from Palace + 1C from city center + xC from tile worked
- 130/10 = 13bpt = 1 +8 +1 + 3
Meaning that they would have to
work a 3C tile from the turn they settle.
Problem : there is no such tile in the area. Even riverside Gold and Gems are only 2C if unimproved.

EDIT: ok now I've looked at the graphs and I'm even more confused.
1/ It's not just OSS, Maple Sporks did the same thing, and it looks like Kakumeika is going the same way.
So it must be something really obvious we're missing

2/ With that being said, I still don't get it.
I took a look at the power graph and it tells us quite a few things :
- +2000 soldiers between T11 and T18 : this can be either a warrior, Hunting, Sailing or AH. The latter two are impossible due to tech requirement, Hunting makes no sense, so
it must be a warrior.
- +3000 soldiers between T18 and T20 : this means
Pop 2, and either
another Warrior or Hunting (which still makes no sense), or Sailing/AH (which still should not be possible). So again, I would say a warrior.
- A score of 47 by T20, if they settled on T1, means
Pop 2 and 2 Ancient techs researched (Poly + ?)
So what all this means is that by T20, they were able to grow to P2 and build two warriors, while researching Poly in 10 turns and another tech, probably Agri.
If we assume that they started with a worker, and that they didn't settle on the corn, then they must have worked a 3F tile to grow this fast after the worker, but then not enough hammers to build those warriors *unless* they settled on either the stone or the marble, but then how did they manage early Poly? ...

...
So I'm inclined to believe that at least one of the above
hypothesis is wrong. Either they settled on the corn or didn't start with a worker. Or something else....I don't know anymore...
EDIT 2 : came back home and tested this, and I'm absolutely clueless about what they did.
I can grow to Pop 2 but not get 2 warriors out by T20 at the same time. Even working the gems from turn 1, Poly takes 11 turns to complete...but then the worker takes 20 turns. How they managed it in 10 turns is beyond me.