He probably got the information from the Chinese BBS.
Andrei Chang, the editor of Kanwa Defense Weekly in Hong Kong, said in a telephone interview on Wednesday that he had been authoritatively told that the jet will make its first test flight on Thursday, weather permitting.
He said Chinese officials appeared to have deliberately allowed word of the tests to become public, even to the point of bringing the jet to a Chengdu airfield, Factory 132 of the city’s aircraft design institute, that is commonly watched by military hobbyists, in a bid to display the nation’s growing military sophistication.