That assumption doesn't seem to be very well supported by the comment you are responding to - what makes you think they don't know what happened in Tiananmen?
We are talking about the people who were crushed by tanks in the square.
Really, most were shot, which is how I'd deal with a trouble maker being filmed like tank man.
But there is evidence of tanks crushing people as per my link, which is WHY tank man is famous (plus he was photographed, other people did do it too).
Are you doubting tanks rolled over and killed people?