Bush talks about EXPLOSIVES in building (on 9/11?)

Bush says this, "For example, Khalid Sheikh Mohammed described the design of planned attacks of buildings inside the U.S. and how operatives were directed to carry them out. That is valuable information for those of us who have the responsibility to protect the American people. He told us the operatives had been instructed to ensure that the explosives went off at a high -- a point that was high enough to prevent people trapped above from escaping."

It sounds eerily like what happened at the WTC on 9/11. Was he referring that the "terrorists" planted explosives in the towers or that foiled plots had planned to use that tactic? Or was he referring to the WTC?
Video of press conference