That's surprising, and the first I'd heard of it! Especially because a ton of people in Japan today seem to consider meat the most enjoyable food group.

https://en.wikipedia.org/wiki/History_of_meat_consumption_in...

Although it sounds like 1. it was only certain classes, 2. it was only part of the year, 3. it still allowed some meat (boar, deer).

As for it being the reason for their longevity... I doubt it's related? Since the ban ended 150 years ago and AFAIK the Japanese longevity is mostly statistics starting around the war I think.