They avoid giving details,
but one reasonable extrapolation from their comments is that censoring "tank man" was intentional, but applying that censorship globally was "poor judgment" which they now label as "human error."
Lots of errors happening lately
And the “human error” always seems to accidentally censor content that some country or organisation has asked to be censored
Or there are a lot of random errors and only the politically sensitive ones make headlines and result in press releases?