I would think your "narrator" was being VERY economical with the truth. For a start I doubt the average life expectancy of dolphins in the wild is 45-50 years, it may be possible for a dolphin to live that long but I think that predation,pollution and the general hardships of life in the wild mean the real figure is much lower. Again, I'm sure there are some parks that don't take as much care as SW/DC do with their animals but I'm sure that SW's dolphins have a much longer lifespan than 5 years, I know that I have seen dolphins that have been at SW for 10-12 years and I think the trainer at DC told me the dolphin that was part of our interaction had been with the SW parks for 18 years.
It's also a fact to be taken into consideration that many of the dolphins in captivity are there because they were rescued from illness/injury caused in the wild, in those cases it isn't suprising that some of them will die from those illnesses/injuries. As is often the case there are , I'm sure well meaning, animal rights activists who will missuse "facts,figures and information" in order to back up there own cause without caring that their deceit weakens the case for those other who care about animal wellfare but see that truthful information, educating the general population and showing them what a shame it would be if those animals slid into extinction is likely to be a much more successful way to ensure our grandchildren get the same opportunity to enjoy and marvel at these creatures that our generation has. JMHO