At the time of that statement (9AM or a minute or two after), he'd just been told about the first hit ("the situation in New York"), and was putting off saying more until his aides had more information (or a script) for him.
From
http://www.unansweredquestions.org/timeline/timeline_dayof911.html(Between 8:46-8:55 a.m.): When Flight 11 hits the WTC at 8:46, Bush's motorcade is crossing the John Ringling Causeway on the way to Booker Elementary from the Colony Beach & Tennis Resort on Longboat Key. < Washington Times, 10/8/02 > Sarasota Magazine claims that Bush is on Highway 301, just north of Main Street when he is told that a plane had crashed in New York City. < Sarasota Magazine, 9/19/01 > Around the same time, news photographer Eric Draper is riding in another car in the motorcade with Press Secretary Ari Fleischer, and overhears Fleischer say on a cell phone, “Oh, my God, I don't believe it. A plane just hit the World Trade Center.” Fleischer is told he will be needed on arrival to discuss reports of the crash. < Christian Science Monitor, 9/17/01 , Albuquerque Tribune, 9/10/02 > Fleischer is told this “just minutes” after the first news reports. < MSNBC, 10/27/02 > Congressman Dan Miller also says he is told about the crash just before meeting Bush at Booker at 8:55. < Sarasota Magazine, 9/19/01 > Some reporters waiting for him to arrive also learn of the crash just minutes after it happens. < CBS, 9/11/02 (B) >
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(8:55 a.m.): Bush's motorcade arrives at Booker Elementary School. <8:46, ABC News, 9/11/02 , 8:55, Washington Times, 10/7/02 , 8:55, Sarasota Magazine, 9/19/01 , “just before 9:00,” Telegraph, 12/16/01 , “shortly before 9:00,” Sarasota Herald-Tribune, 9/10/02 , “just before 9:00,” New York Times, 9/16/01 , 9:00, Albuquerque Tribune, 9/10/02 > The trip is said to take 20 minutes, which confirms he arrives around 8:55, if it is true he left around 8:35. < New York Times, 9/16/01 , St. Petersburg Times, 9/8/02 (B) , MSNBC, 10/27/02 >
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(Between 8:55-9:00 a.m.): Just after Bush arrives at Booker Elementary School and is briefly told of the WTC crash, he is whisked into a holding room and updated on the situation via telephone by National Security Advisor Rice. < Christian Science Monitor, 9/17/01 , > Rice later claims, “He said, what a terrible, it sounds like a terrible accident. Keep me informed.” < ABC News, 9/11/02 > School principal Gwen Tose-Rigell is then summoned to a room to talk with the President: “He said a commercial plane has hit the World Trade Center, and we're going to go ahead and go on, we're going on to do the reading thing anyway.” < Associated Press, 8/19/02 (D) > One local reporter notes that at this point, “He could and arguably should have left Emma E. Booker Elementary School immediately, gotten onto Air Force One and left Sarasota without a moment's delay.” < Sarasota Herald-Tribune, 9/12/01 (B) >