There was never a conclusion that certain sleep lengths lead to decreased life span, only a correlation. The causal link has been suggested to be the reverse -

There was never a conclusion that certain sleep lengths lead to decreased life span, only a correlation. The causal link has been suggested to be the reverse - that sick people tend to stay in bed longer because they're sick. I believe I saw a recent article that even said that the popular takeaway that avoiding "oversleep" is healthy is the opposite of reality, because extended sleep is actually a healing mechanism.