If you’d prefer, we can call it unclassified communication rather than personal communication. The point is that it was not used for Secret, Top Secret, or other classified communications. For that, he had the SME-PED device.
So, again, it’s not a parallel to the current situation. Nobody is saying the SecDef and other staff shouldn’t have unclassified devices as well as their classified devices, the issue is that they’ve been using the unclassified devices to conduct Secret or Top Secret discussions.