Having carbon fiber scales or other materials that are not detectable by metal detectors would not make a knife illegal under the law as written.
If the knife has a metal blade and non-magnetic everything else, it would NOT be undetectable by a metal detector.
Likewise, if a knife has a ceramic or plastic blade that is not detectable by a metal detector, but has metal liners, scales, locking mechanisms, etc., then the knife would NOT be illegal since the non-blade metal components would be detectable.
The only knives that would be deemed illegal under this law would be those knives constructed of only non-metal detector components, i.e., non-magnetic blades, non-magnetic liners/bolsters/scales/screws/nuts/clips.