Are larger people that don't work out stronger than skinny people that don't work out?
Yes and no...
They are generally stronger, but not because of what you probably think.
They're stronger because of Physics...yup...Physics.
They have more weight as a counterbalance, they have more size to leverage more and they can build more momentum to move something heavier to a stationary position.
Example...look at Olympic style weightlifters...I'm not saying they have no strength or muscle but if you look at their motion you'll see the difference.