The players running the triangle were using the NIC income to buy ore for production.
The purchase of ore wasn't wholly dependant on them selling modules, so they could continue having a demand on the ore sales independant of the marketing of goods.
When they lost that NIC source, they no longer had the funds to purchase ore independantly, so demand for ore dropped; Lower demand, lower prices.
In general, the market is so small that individuals can have a dramatic effect on the prices, especially T4 which has a limited number of suppliers. That is, there are more players mining for income, so individual players can't adjust titan ore prices (they can move them down by flooding the market) upwards. It is possible though for T4 producers to do so, simply by matching current prices, or by putting them up for more then market and waiting.
tl;dr - The population and market are too small to apply any real ecomomic analysis, but in general supply and demand drives the ore market while modules/bots can be more readily manipulated.
Market can be easily influenced by corporations.
During the Great War against M2S CIR & CHAOS did organized market-warfare to raise epriton price through the roof (when we still thought they were playing "legit" and buying everything off the market). If memory serves we skyrocketed it from 11 NIC p/u to 16+ NIC p/u by pouring a few hundred million NIC into setting up buy orders on a rotation schedule.
