I don't know the details of the problem they had, but if they were having problems with just one of the pressurization controllers, then a diversion would not be needed. But if they had lost both (or one was deferred and the other one bit the dust here), then I can understand the diversion.
The CRJ has 2 controllers, but only 1 is active. They trade after every flight, or if 1 fails the other automatically jumps in. But in the unlikely event that both are lost, the flight can be continued in a manual pressurization mode (which isn't all that difficult, it just requires keeping an eye on it and changing as you climb/descend)