It didn't seem to be based on evidence at the time rather than a simple minded and racist bit to cover up that he had no idea what he was doing.
I'm speculating of course but if you think about it, can you imagine him sitting patiently reading documents first thing in the morning? He would get bored so quickly he would end up on twitter to complain or gloat.
If your intention is to motivate Americans away from Chinese products, what better way to do it then to use a scary virus that seemed to emerge from China to that end.