If I recall correctly, law enforcement also used a SPEV talkgroup for the MS Bike Ride back in September.
Law Enforcement and Fire each have their own, different, special events channels. You are right, special event channels can be used for other things like the bike ride, training, damage assessment after a storm, etc, which is why I stated 99.9% of the time they are used for training.
W9NES is correct, if its a true, working incident, 99% of the time it will be placed on an actual Fire Ground