I disagree.
I disagree because it's applying the answer for one problem to another unrelated question.
The '5 threads' rule appears in Article 500 simply because there needs to be a flame path that long to assure that an internal explosion does not ignite the atmosphere outside the conduit. The requirement has nothing to do with grounding.
As for grounding, the UL research study that evaluated the use of conduit as a grounding means included -more by accident than design- a number of poor connections. No matter- the pipe proved to be a fabulous conductor.
Remember the EMT fittings that were once 'crimped' on? Now, there's a loose connection for you! Yet, it somehow managed to work.
Just as important, there are several instances in electrical work where a tapered thread is connected to a straight thread. It's simply not possible to fully engage 'five threads' in that situation; EVERY coupling would be a violation.
