If the corals weren't acclimated to the temperature or it changed quickly, absolutely.
I keep my tank "cold" at around 74-76. I've heard so many horror stories about exploding and malfunctioning heaters that I pulled them out of ALL my tanks. I have to keep the house warm for my parrots, so, all in all it works out very well, and it's one less piece of equipment I have to worry about!