Copper oxide reacts with sulfuric acid to form copper sulfate. The color of copper sulfate is dependent on the degree of hydration. The blue crystals of copper sulfate that are usually seen are crystals of the pentahydrate form CuSO4.5H20
If the hydrated copper sulfate is heated further and the water is evaporated gradually, the resulting form of copper sulfate turns a pale green and finally turns white in color.
In the procedure followed by the student that you have described, the white compound that was formed is due to the student's mistake of heating the filtrate to dryness. This converted the pentahydrate form to anhydrous copper sulfate which is a white colored compound.