Wow, that is too bad... and probably the man didn't even know he was at risk. Heart attacks and strokes can happen at anytime, anywhere... without notice, or even provocation, so the fact that he had just exited Big Thunder most likely had nothing to do with it. It could have easily happened on the Carousel, or just walking through the park. I feel for his family, loosing a loved one so close to the holidays, in such an unexpected way.
Also, they will likely never look at a trip to DL in quite the same way again.