Its really difficult to lose weight without exercise because the only way you can lose weight is if you burn more calories than you consume.
Its difficult to do that by eating right because your calorie intake will have to be very low (and perhaps unhealthy) unless you actively burn calories in other ways, like a job that requires a high level of physical activity.
I wouldn't doubt someone if they said it was possible, but I would say its very difficult and not the best/safest solution if it works.
Not only that but you can never leave that diet. Working out will create muscle which burns fat and will allow you to eat more without gaining weight since you can burn more calories in general.