To clarify, it's the physical distance between the imager and the lens' point of convergence (shown below). So in the case of your two lenses, the focal length is simply somewhere in the middle of the lens. Most lenses are made up of several elements (also shown below) and the convergence point hits at one of these elements.
In the case of the Fuji camera, I'm not 100% sure what they're doing there. They could be using a telephoto converter in their lens, which magnifies the center portion of the image to increase the effective focal length. They're common in photography, though they are available in surveillance as well. We will see what we can find out.
Onetime I have asked professional optical laboratory to measure actual focal length of some very expensive FA lenses. Actual value varies up to 10%. What could we expect from those cheap used in cctv ?
A year or so ago, someone posted a great video showing how to properly specify lenses and configure the FOV (depth of field?). The video showed a man walking a very long distance in a parking lot towards the camera - in the first poorly configured example, the man was indistinguishable until he was very close to the camera and the distance he walked looked really long. In the properly configured view, the depth of the parking lot looked shallower and the man appeared to walk forever even though it was the same distance and the image at all depths was crystal clear.
If this sounds familiar, I'd love to see that video/link again. I think the person who posted it was a Consultant.