In a way, they could have been doing that - trying to rob Peter to pay Paul. While in theory there are reserves, it could be that on that day and airplane type there were no reserves available in CLT. The next step would be either get someone from another base or take someone off another trip to fill in and shorten the delay. There's also the possibility that scheduling was calling blockholders trying to find someone to fill in on their off day(s).
And the whole thing could have involved the east/west flying split, making it harder to find a quick replacement.
Jim