O'Reilly writes that "many were killed" during the riot. The CBS News report from the riot does not mention any deaths.
Because the Argentine government blacked out the news and refused to release fatalities to the press, but later admitted that there were deaths after CBS filed it's report.
Or there were no fatalities to report. There is no proof either way, plus there is no proof O'Lielly was still there when the demonstrations turned to rioting, since CBS kicked him out in short order after his firat encounter with the demonstrations.
Link
CBS kicked O Reilly out of Argentina The Ave
“The CBS bureau chief in Buenos Aires, Larry Doyle, an ex-Marine LRRP, was something of a legend among CBSers because of his personal courage and his knowledge about how to do your job without exposing yourself to undue danger. Early that night in Buenos Aires he assembled the camera crews in our hotel newsroom and instructed them to refrain from using the lights on their cameras while around crowds. Television lights attracted potentially violent people and also made the camera-person an easier target for demonstrators throwing rocks. …
“According to Doyle, O’Reilly returned to the hotel in a rage over the fact that his cameraman wouldn’t turn on the lights to photograph angry crowds. Doyle defended the cameraman and chewed out O’Reilly for violating his instructions on lights. When Doyle looked at the tape shot by O’Reilly’s cameraman he saw that … O’Reilly had ordered the cameraman to shoot — with his light on. …
“[T]he demonstrations … had been well covered by three or four camera crews …. All that footage was blended into the main story, narrated by Schieffer, who [was] the anchor on the scene. When Doyle informed O’Reilly that Schieffer would be doing the report … the reporter exploded. ‘I didn’t come down here to have my footage used by that old man,’ he shouted. Doyle was stunned. … This confrontation
led the next day to O’Reilly being ordered out of Argentina by the CBS bosses. … ”