My understanding is that China conducted two tests - one of which you link to. Worthy of note is that both tests were on live subjects - seen in the village around the test - interestingly both villages were Chinese muslim.
Images were taken by US spy satellites which watch for such events - no foreknowledge necessary.
The original report was from a site having the name Security in it - I do not remember the full name, but I think I went looking years ago and it is now a pay site. It gave further images and a full analysis, appearing in the year of the test.
Are you referring to GlobalSecurity.org? You can get around the page visitation limit by typing the subject in a search engine, then just look at the “cached page” next to your search results.