I didn't load up the save but I'd imagine the Iroquois have a decent sized landmass spammed with cities, a nice population, and are cranking research at a good clip. Probably has some maritime allies for food/pop boost.
Iroquios are fun to play - I like to TP forests or build LMs and with longhouses both get to be ridiculous for production if you have a lot of forests around (which also makes for less road building for them so you build up more gold too).
Iroquois also often seem to be like france as AIs roll - they often end up with huge empires via conquest. Kinda funny, they both act all friendly and cooperative but both tend to shred other AIs to expand. Usually if I'm early and seeing other unmet civs/CS fall a lot, it's the french or iroquois who are responsible.
The AI sucks at tactical combat, but a lot of other aspects of the AI are very good.
For ex, the AI seems to be very smart about knowing it has an isolated start and takes advantage of it like a player would.
I've seen an isolated babylon with 7 acadamies (posted an SS here about it a while back).
I've also seen runaway AIs with 25+ tech leads on me when I'm doing pretty well, so it's not really surprising.