It is a combination of things. Part of it is production and culture just didn't get built until after turn 170, part of it is the land around him was actually pretty poor, with no mountains, only a few short rivers, and lots of space with no fresh water access (and I was shocked at how many water poor cities he founded). The other part of the problem is he doesn't harvest/clear/chop before popping districts down, and that hurts his growth and production a lot.
But yeah, he also didn't spread out enough. Taking the full 6 spaces between cities isn't always ideal, but several of his cities are bare minimum apart and left a lot of dead space for barbarians to spawn in. Also rather importantly (and Marbozir also does this, though he prefers keeping units in cities.) prefers keeping units in odd spots, rather than to reveal stuff out of sight and prevent barbarians from spawning. There are several areas that would have benefited from a military presence on the borders to either keep barbarians from spawning, or fight the hordes as the come in. Instead they just wander in and pillage stuff.