Non-researcher here, but does this imply that China is doing significantly more research than the other countries mentioned? I'd imagine it's either that, or the 'legal' article access systems aren't as accessible?
> maybe there's some students who are randomly downloading all papers they're interested in?
You pretty much have to operate that way anyway. There is just too much stuff to do the old-fashioned “read one paper, get its references, and repeat”. It is much better to get many articles, and then sort them by degree of interest using things like abstracts, main figures, conclusions, etc, before reading them fully. It does increase the number of downloads significantly.