Because coal pollution isn't listed as a cause of death (just like all pollution). It raises the incidence of many other diseases, and those diseases are listed as the cause of death. Coal also has additional direct deaths in e.g., mining accidents.

The numbers are nice round numbers because, well, there are somewhat imprecise. Looking up actual studies that came up with them would give methodology & margins of error.

Compare to, for example, smoking. The cause of death will be e.g., lung cancer. But had he not smoked for 30 years, he probably would have lived longer.