I also agree on the stressful work part, but don't quite understand what you mean with "lots of commute on public transit". If you mean the Tokyo-style rush hour traffic where people are literally shoved into the train car, of course that's stressful. But at any other time apart from that, Japan's public transit is enormously soothing and stress-free, both because of culture and transit technology.
As a result, public life itself is more quiet and soothing, because you are not constantly surrounded by cars, even if just sitting outside a café.
As for the family you stayed at, they must eat differently from the Japanese families I know personally. Studies agree: https://www.livescience.com/54133-japanese-diet-longer-life.... https://chns.cpc.unc.edu/resources/publications/bib/2884/
there's plenty of great home style food that isn't fried.. nikujaga, gyusuji, nikudofu, etc.
Public transit there is pretty great. If anything the lack of escalators for some stations can be unmotivating to some people but on the other hand walking a lot of flights of stairs is healthy.
Corrected that for you.
But lots of walking in their less elderly days may partially explain their longevity.