Who's claiming that living inside the boundaries of such zones would confer health benefits?
The paper is pointing out that if you actually look at the data there is nothing remarkable about the region's average lifespan (actually lower than the entire country of Japan), which is what's being discussed here.
That's my point -- the region's average lifespan is irrelevant. It's only relevant given the misconception that Loma Linda itself has some special properties of rejuvenation.
But that doesn't mean it's not a longevity hotspot. Even if the average lifespan there were lower than normal -- say a large number of unhealthy people lived there -- it still wouldn't negate that, if an abnormally high number of healthy centenarians also live there.
"Loma Linda residents have some of the highest lifespans in the world."
"Well it turns out they actually just have average lifespans."
"Only true Loma Linda residents have the highest lifespans."
If you discount everyone who died at a normal age, you can conclude that Loma Linda residents are doing something special.
Just kidding. But more seriously, the original claim was deeply flawed so it makes sense to challenge the criteria for the population study.