That seems like a calories in = calories out type CW statement: "can't build muscle without extra calories" bah.
The body is too complex to state it like that. Building or loss of muscle, bone and adipose tissue are all hormonally controlled! You've changed your exercise, and therefor changed what your body does with the fuel and building blocks you give it. So the hormonal signals have changed! So I don't doubt you can gain muscle and/or bone mass without nutritional changes but only the exercise input changes.
You were giving your body the materials and fuel all along, you've just changed how you are swinging your hammer! Now you are hitting some nails and perhaps building more muscle and bone!
I'd also love to know the weight difference of bone before and after an exercise program. How much does a human skeleton weigh, anyway?
Don't forget more blood, too. I've heard (??) that regular exercisers generally have about a quart more blood over non-exercisers of the same weight.