You answer:

Accumulating that many crystals in just two weeks without donating sounds unrealistic. Even with active play and participation in all events, rewards usually don't provide that much. Most likely, the player is either hiding something or using third-party replenishment methods. Many are currently solving the resource shortage problem with services like Kingshot recharge which allow for profitable balance replenishment without unnecessary costs and risks. So it's entirely possible that the player used something similar and simply didn't tell others about it.