[Tomte]

est probably means that while we "know" that people were killed on Tiananmen Square, they were actually killed in the streets around the square, not on the square itself.

(Other sources say that there were indeed deaths on the square, but less than five or so, not the main massacre)

But it doesn't really matter where exactly the deaths happened.

Only insofar as it reminds us of the fallibility of the human mind (cf. witnesses in court): many people actually believe they have seen in TV how people were slaughtered on the square, which is demonstrably incorrect.