It's quite true. Computer farms have a distinct signature in terms of building. They require temperature controlled buildings with heavy duty power sources running into them. Also, if the Chinese were building new computer farms right now, US sats will see them under construction, and mark their locations.
This might be a fair point if you were looking in a very undeveloped developing country, where you suddenly had such a structure in the middle of the desert or by some mud brick buildings etc.
But this is China! a huge country with a huge and high tech manufacturing base. There are dozens of advanced manufacturing processes that possess the same requirements as you state above, most of them Electronics and now increasingly, Bio-Mechanical/Medical Science centers.
Most of these Industries tend to cluster for obvious economic reasons in the big Industrial Zones of the Coastal Provinces and it very obviously in such places that a Computer Farm would be hidden.
Anybody who has ever visited a Chinese Industrial Zone, will realise that how huge the places are and just how many of them there are. Unless you had very precise intelligence as to where these facilities were, you would be looking for the proverbial needle in a haystack.