There are some pools that reroute the computational power, depending on where they can make the most money, i.e., they maximize their utility for a fixed amount of hashing power. Apparently the huge influx of computational power triggered these automatic coin choice pools to switch to the Feathercoin network, which again triggered more pools to switch.

In the end, the attacker not only had to fight against the computational power of FC, but also had to deal with the power coming from those pools, which proved to be too much, and he lost his majority.