If we decrease premature deaths from any cause, particularly a common cause of premature deaths, we increase life expectancy. Or just what do the authors think life expectancy means? It's an average. Every premature death drags down average life expectancy.

If we say that cancer screening has no effect of life expectancy, that's exactly the same as saying that it doesn't prevent premature deaths.

If cancer screening effectively prevents premature deaths, but the effect on the population's life expectancy is small, that effect is the wrong thing to be focusing on, potentially resulting in a harmful takeaway message.