After reading the japanese forums and recent dev posts, I think they are purging RMT, botters, cheaters and related things to them atm and will post their results soon. At least on Ultros there was just 1 teleport bot left in Thanalan. The bulk of lvl 1 miner bots were trying to "blend in" and, using terrible pathfinding, look for nodes "manually".
So my wild guess would be that SE was cutting the RMT gil from the economy and some people got so much of that gil that if removed, they would go minus gil, hence the /100 that happened.