The idea is that this diet was developed based on the foods eaten in Ancient Greece. However, many of the foods recommended in the modern version of this diet were never available in Ancient Greece. There are lots of good things about this diet like eating a lot of fruits and vegetables, nuts, and whole grains. They recommend using more spices and less salt. Most famously, they recommend using olive oil instead of butter. However, with no advice to limit the amount of olive oil which has about 140 Calories per tablespoon, this advice can sabotage your weight loss plan. Many people just add olive oil to their diet and think they are on a Mediterranean Diet.
Learn more about diet myths at https://www.uclahealth.org/clinicalnutrition/nutrition-fact-or-fiction