The paper doesn't even use it consistently. At first it uses "all-cause mortality" to mean "all causes except COVID", and then in the results section it uses the same phrase to mean "all causes including COVID". The whole purpose of terms of art is to increase the specificity of language, but they're not doing that here. Their usage of the term is confusing.
Edit: I'm wrong. I could have sworn it said that the groups had similar all-cause mortality, but it doesn't.
Where do you see them using "all-cause mortality" to mean "all causes except COVID" in the beginning? I skimmed over all uses of the term before the "Results" chapter, none of them seem to exclude COVID deaths?
Edit: I'm wrong. I could have sworn it said that the groups had similar all-cause mortality, but it doesn't.