That's the opposite. Your protecting the cable from being manipulated. OP is talking about protecting the cable from being read.

The problem isn't that they were keeping a USB cable in a secured location for security concerns, the problem was that they were doing so because they believed bits were left over in the copper itself and enough such that data would be recoverable. Like marbles through a tube.

I do hope the practice was due to your point and that the particular person was just naive, misinterpreting a presumably shitty PowerPoint.