There's more. In
this QA NIST clarifies the scope and reasoning of the previous assertion in more detail. The relevant excerpt (trying to be brief, but not to misquote, go to the link to verify):
In the draft WTC 7 report [...], NIST stated that the north face of the building descended 18 stories (the portion of the collapse visible in the video) in 5.4 seconds [...]. This time period is 40 percent longer than the 3.9 seconds this process would have taken if the north face of the building had descended solely under free fall conditions.
[...]
The analyses of the video [...] revealed three distinct stages characterizing the 5.4 seconds of collapse:
* Stage 1 (0 to 1.75 seconds): acceleration less than that of gravity (i.e., slower than free fall).
* Stage 2 (1.75 to 4.0 seconds): gravitational acceleration (free fall)
* Stage 3 (4.0 to 5.4 seconds): decreased acceleration, again less than that of gravity
This analysis showed that the 40 percent longer descent time—compared to the 3.9 second free fall time—was due primarily to Stage 1, which corresponded to the buckling of the exterior columns in the lower stories of the north face. During Stage 2, the north face descended essentially in free fall, indicating negligible support from the structure below.
So Christopher7 is applying a quote with a scope which covers the first 5.4 seconds as a whole, to the second stage where the building fell "essentially in free fall" (which is not the same as "exactly in free fall", no matter how often he tries to push that).