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?
It's a lot less charitable than "OP was probably referring to the fact that video evidence shows tank guy being pulled away out of sight before the tanks continued past the point where he had been standing, rather than showing the tanks just rolling over him as that comment kind of implied". If you're going to be very careful to correct people who assert that the guy wasn't crushed, you need to jump on people who say he was crushed too, or you look like you're using the argument as an excuse to attack someone rather than being deeply invested in correctness.