Mediterranean diet significantly reduces the risk of mortality in elderly people

From here: 

Following a Mediterranean diet can extend a person's lifespan and reduce the risk of mortality in elderly people, according to a new study.

Italian researchers from the Department of Epidemiology and Prevention of the IRCCS Neuromed, in Molise, Italy, analysing the relationship between a traditional Mediterranean diet and mortality found the life-prolonging link when studying participants over the age of 65 who adhered to the diet.

According to the findings, the diet, comprised of a mix of fruit, vegetables, fish, olive oil, and moderate wine consumption, is associated with a 25 per cent reduction of “all-cause mortality” and the effect remains when considering “cardiovascular or cerebrovascular mortality” as well.

Well, at least I eat plenty of fish and olive oil and nuts.  But very little in terms of vegetables and fruit (unless potatoes count), and no wine (although I drink lots of lager).

Similar to those who claim that studies reveal consuming 5 to 10 portions of fruit and vegetables a day will help prevent heart disease, diabetes and some cancers, and hence extends one's life, I would like to know how they know it's the consumption of these foods that are of primary importance rather than the avoidance of ultra-processed/junk foods?  That is to say, perhaps it's not so much what you eat, but what you don't eat?  I do not believe that studies distinguish between these 2 possibilities since eating through humongous amounts of vegetables and fruit every day will leave very little appetite for any junk foods.