He is very obviously referring to the 1993 WTC bombing that was orchestrated by Khalid Sheikh Mohammed, the same guy that oversaw the 9/11 attacks. Its like "truthers" are incapable of taking in and processing very easy to understand information. They just look for keywords and then morph it into their head to mean something totally different for their god awful confirmation bias.

"dont forget that took a big bomb in the basement...and it withstood that and I got to see that about three of four days after it took" is what he says.