He literally said it contributes. Possibly the very first thing that was concluded about COVID was that if you're obese, or whatever else, then you're likely going to have a harder time with the virus. But what you are suggesting -that Trump should talk about dietary improvements, etc.- is asinine as all hell. What's Trump going to do? Put a link to Weight Watchers in a tweet? How on Earth can losing weight, if you are a chronically obese individual, be compared to looping a piece of fabric around your ears when you're in public? If every single overweight person in America, hypothetically, were to start hardcore dieting today, it would likely be at least a year before the majority of them start to approach safe weights. Compare that, to, wearing a mask. One is an instantaneous solution, that one can do TODAY. the other is something that you can achieve over the course of several months, or likely even years, by which time hopefully this disease will no longer be so relevant.
Furthermore, being obese affects you and only you. Wearing a mask, and practicing social distancing prevents you from giving the disease to others, regardless of how badly it affects you. THAT's what's important.