I mean, it was almost certainly an “organized scheme.” But was a genuinely grass-roots scheme by genuine Chinese sci-fi fans, or was it a scheme by the Chinese government? I’m sure it had at least “tacit” governmental support, in that Chinese censors didn’t squash it. But beyond that…I don’t know it for sure it wasn’t some sort of government-backed scheme, of course, but, again, that explanation just doesn’t seem necessary to me. The only other bid was from a group in Winnipeg. And Chengdu is a city of over 16 million people. You could probably rustle up a couple of thousand votes from just sci-fi fans and local businesses in Chengdu alone without much problem. Dublin, Helsinki, and Glasgow have hosted Worldcons; Melbourne has managed to snag it four times, without any accusations of meddling by the Australian government that I’m aware of.
It’s certainly possible that the Chinese government schemed to get a small geek convention, but it also seems very plausible to me that in the most populous country in the world all of a couple of thousand of sci-fi fans managed to self-organize a campaign to finally get a Worldcon.