I applaud him for trying to find a way to build a CITY that was designed to be as self supporting and non polluting as possible. China happens to be the place where it might have been possible; especially since as you say the farmers are often left much worse off than before once a developer moves in. I doubt very much he chose that site himself, btw, it seems likely he was likely given a choice of a few sites and settled on that one just as he was given a choice of builders. Who knows what options he had? Anyway. China also has the cash to build such a project; few other economies have that these days. As you said, Green is a buzzword over there (though it seems likely it means as much as civil rights, i.e nothing at all) So it would be relatively easy to fall into the trap of thinking they were serious.
He may have been naive; it seems quite probably that was the case. OTOH if nobody ever tries, if nobody ever trusts, then no progress would ever be made. Also, the bolder the effort the more of a target it makes. People love to target shoot.
If you watch as many of the TED talks (and related articles) as I do, then you would see that what he planned was infinitely more sustainable and human friendly than is generally the case. I have seen stats on just what the future appears to hold and it is not a happy prospect; already millions of people are living in substandard slums (there are slums and then there are these, as well as the thousands living in refugee camps) throughout the world. Something like 2 million people don't get enough to eat on a daily basis. And, as you noted, there are people daily leaving the country to find their fortunes in the city. So cities are growing like crazy, all over the world, and almost all of them have areas for those who haven't been able to find work at least that allows for a decent place to live or standard of living. So.
One of the things that has shown up is that as the standard of living goes down, generally speaking, people have more kids. It's a biological thing; if people live precarious lives, (not of their own choosing, that is, not talking about people who like to climb skyscrapers on the outside without safety gear or who try to jump the Grand Canyon on a motorcycle) they tend to have kids so they leave someone to replace them. Lots of kids supposedly increases the chances that at least one will live to adulthood. Possibly also so few other options for entertainment are available that at least there's always sex. Maybe they just can't afford birth control or it's contrary to their culture, religion or whatever.. (Not talking about China here). Lots of people are planning cities to hold these people and their following generations and many of the plans seem to be ignoring anything even as basic as green roofs or solar orientation presumably because the scale is so big they can't deal with it.
Many will have one or two special showcase buildings which are solar oriented and which would be relied upon as food producers as most of them assume they will feed people with food hydroponically grown under artificial lights, so there is little or no concern about farmers or green space at all. I haven't seen any which planned for the sewage to be used to produce natural gas and compost to supply the city's energy needs, as his did. I haven't seen any plans which involved replacing the appropriated farmland by moving it onto the roofs of the buildings, as his did. Etc. Maybe they're out there, but I haven't run across them.
So yes, although I concede he may have been naive to think that such a plan would actually be followed through on, I do applaud him for trying to meet the challenges of the future by trying to plan a sustainable city. The fact that it was to built in China was immaterial to the prospect of having it built at all, China could have led the way.