It is very difficult to say what this study actually found from this excerpt.
A confounder of studies such as this is that people who are terminally ill often lose a lot of weight before they die. So, even though obesity may not be very healthy, a study could show that obese or overweight people have a better prognosis—even though if compared with healthy, non-terminal people, they may actually be pretty bad off.
people that smoke cigarettes have suppressed appetite, meth addicts and cocaine addicts don’t eat either, all can be real thin, Karen Carpenter starved herself to death, so ye, being too thin can be deadly
But fat people have multiple health issues too.