Are you referring to a report in The Times? If so, it's behind a paywall so I cannot read the article but I too doubt that loneliess is the official cause of death.
That said the CDC (Centres for Disease Control and Prevention) write:
Although it’s hard to measure social isolation and loneliness precisely, there is strong evidence that many adults aged 50 and older are socially isolated or lonely in ways that put their health at risk. Recent studies found that:
Social isolation significantly increased a person’s risk of premature death from all causes, a risk that may rival those of smoking, obesity, and physical inactivity.
Social isolation was associated with about a 50% percent increased risk of dementia.
Poor social relationships (characterized by social isolation or loneliness) was associated with a 29% increased risk of heart disease and a 32% increased risk of stroke.
Loneliness was associated with higher rates of depression, anxiety, and suicide.
Loneliness among heart failure patients was associated with a nearly 4 times increased risk of death, 68% increased risk of hospitalization, and 57% increased risk of emergency department visits.
I think we know this, don't we and why is it so important to try maintain social contact. The negative health effects of isolation during the pandemic have been well documented.