I talked with our engineering department and this is the answer I received about the YouTube video.
Concerning lock strength in knives, it is most practical and convenient to measure torque about the pivot of a folding knife using in-lbs. The main reason is that the average knife handle is around 4 inches long, and the force applied when prying or putting weight against the lock is distributed more or less evenly across the length of the handle. This can be simulated by applying a single point load half way along the handle (ie. 2" from the pivot).
The calculation for torque is this:
T (Torque around the pivot) = F (Force applied) X D (Distance from where the force is applied to the pivot)
For this equation to be valid, the distance must be consistent. Since we measure the distance to the pivot in inches, the resulting torque must also be In-Lbs, not Ft-Lbs.
In practical terms, 600 in-lbs of torque is the equivalent of having to apply 300 lbs of force to the handle. Most users would not be capable of applying that much force to a knife.
Typically ft-lbs would be used to measure something with a longer fulcrum arm, like a crowbar, not a knife.