Is there any difference between theoretical and mathematical? In computer science, is there any difference in usage of the terms: theoretical, mathematical?
If yes, which is more broader?
Context: If my supervisor says focus on theoretical aspects of the paper  and focus on mathematical aspects of the paper. Should I interpret as same?
Theoretical and mathematical: They're different. Mathematical aspects are the mathematical parts, whereas theoretical aspects are the fundamental computer science parts. E.g., computational complexity is theoretical computer science, whereas statistical analysis is mathematical.
That said, it may depend on the context. Ask your advisor for clarity.
Ask your advisor for clarity whenever you don't understand, or, at least, mention that you don't understand and that you'll look into the details later, possibly asking for direction on where to look.