People with health problems are told by their doctors to stop drinking alcohol.

From TFA:

"An analysis from 2007 by an international group of alcohol epidemiologists and addiction researchers, published in Annals of Epidemiology, notes that “as people progress into late middle and old age, their consumption of alcohol declines in tandem with ill health, frailty, dementia, and/or use of medications.” That decline means that, as people become less well—even if they’re not elderly—they will also tend to stop drinking."

I might have been too subtle since you TFA so nicely.

The article points to adverse health related events that cause abstainment. Clear and good the AoE-article works that out.

I however point out that it's pretty clear within the drinking categories you have effects that go in tandem with other illnesses as well (like self-medicating with alcohol for psychological issues).

So the whole argument they propose should at least be carried out to its full, working both ways. You've got illnesses moving people into abstainment and illnesses moving people into moderate or high alcohol usuage. The only way to control this is to use changes in comorbidity over time as a factor.

TBH the scientists in the underlying article write this down as an issue as well.

Right, I mis-summarized the article. A more accurate summary would be: non-drinkers are more likely to have pre-existing health problems than light-moderate drinkers.