The difference is covered vs uncovered and both can occur in either personnel group.
The logic behind this rumor/argument is Cam lacks the size to go up against bigger nose tackles but his ability to get out and pull sets him above the others.
Fwiw, I don’t for a minute buy this argument. Continuity along the line and the center’s role in making calls is too vital to play musical chairs. It would also be way too easy for teams to change fronts to dictate personnel and play calls.