Halon............apart from it's secondary use of starving fire of oxygen, the small MOD issue green halon extinguishers were excellent for mouse extermination in the long Kesh towers :innocent
I would hazard a guess the fire was in the roof void & the panels were assumed (the crews dynamic risk assessment would i expect say the panels are to be taken as a still live voltage) to be still live so yes the crew would have probably used CO2 to kill the flame them powder to smother ensuring no reignition, they would then have allowed somebody in to isolate the system.
I've seen one of our (older) experienced crews use both types of extinguisher at the same time with the nozzles close, this spreads the powder over a wider area & knocks over the flame pdq, very messy but effective.