Sounds like this is a "preventative measure".
Normally there is some time between neutron capture and actual nuclear fission (I have heard a figure of 15 minutes). This means that even if the control rods are slammed in when the power transmission lines were cut the previous heat load would still be generated for a period of time. Often this means resorting to drastic measures to reduce the neutron flux to zero ASAP (certain salts are added to cooling loops which achieve this but requires a good flush to get rid of).
Controlled shutdown means the reactor can be restarted in "a couple of hours"
Emergency shutdown means the reactor can be restarted in "a couple of weeks"
Burnt once, twice shy...