Answer: Smoke will NEVER activate (open) a sprinkler head. Sprinkler heads are designed to be activated by heat, each head having a target temperature and flow, designed for the property type they are being installed in.
Smoke can, will, and does activate smoke detectors. Thus, the need to wake everyone up at the hotels...
(Some properties do have systems that will charge sprinler systems, in high hazard properties when smoke or an unusual rise in temperature is sensed. The Expo center did not appear to have this type of system.)
That being said, one could assume that the smoke detectors were turned off during the event.