Airbus girls post is a good explanation, except that if a crew isn't cat 3b qualified they don't only have the option of cat 1 or greater minima.
Depending on aircraft limitations they could be trained for cat3a (50ft decision height and 200m RVR) or cat 2 (100ft decision height and 300m RVR).
Flybe dash 8 aircraft are cat 2 certified so that is what the crews are trained for. However this is a manual landing after disconnecting the autopilot at 80ft, and as such is a little harder than the task of monitoring an autoland. (before anyone asks, yes I have done both). Because of that there is the requirement for 100 hrs on type for captains before they can fly actual cat 2 landings, to enable them to get the feel for the aircraft before they have to wrestle it to the ground with possibly an 18 knot crosswind whilst potentially being able to see jack sh*t except for a few runway lights in the fog.
Bombardier did offer an option of manual cat 3 on the dash 8 with a head up display, but the figure bandied about was about 1 million dollars per aircraft, and despite what passengers may say on here, for an airline ordering 60 aircraft a saving of 60 million dollars will go a long way towards paying for a few diversions each year when cat 2 isn't good enough.
I would agree that the captain in question probably does deserve his red face, not as has been suggested for not being qualified, or for operating his aircraft in accordance with company SOPs and JAR/Eu Ops requirements, but as has been said, for giving the passengers to much information.