I completely agree with everything in this post, except that "complications of a fall" certainly can be related to lack of fitness, specifically in that loss of muscle mass as we age is an important risk factor in falls.
But, as I said I still agree with your post. Everyone, even that healthiest people, have some chance of death at any point in time, and that chance increases with age for all of us. Fitness can mitigate that, but no one thinks it's a panacea, and 76 isn't all that young. If there were some data that people who followed his exercise advice died at a younger age than average that might be suggestive of something (I'd actually guess it was just because he was marketing to already unhealthy people who were getting healthier but still not enough to reach the population average), but a single data point isn't going to tell me much. That he died a couple of years younger than average isn't compelling evidence of anything.
And, yeah, as you say he may not even have been following his own advice.