Just because you "try your best" to eat healthy doesn't mean you can throw out decades of nutritional studies.
Look, it doesn't matter how many sugary drinks your acquaintances gulp down every day, what matters in the end is how many calories they burn compared to you.
If you work out once a day and the rest of your time is spent at a desk in near-immobility, while they have a physically active job, then they're going to burn more calories than you. Regardless if you work out and don't drink soda.
The only logical conclusion is that you're somehow ingesting more calories than you need and burning less than you should (if your goal is to be thinner).
It doesn't matter if you believe you are "doing it better". It's simply physically impossible for you to consume less calories and stay fatter.
So yes, it is all in the foods consumed.
Of course, this does not mean they are healthier than you, but it also does not mean you are healthier, or that drinking 8 sugary drinks per day is conducive to being as thin as they are.