I knew so far that, the classification of crust as SiAl-SiMa, vs. classification of crust as Continental-Oceanic; are completely different, as told in my school geography and university paleobiology class. (However I'm not a geology student)
Where Continental crust and oceanic crust placed side-by-side, so, no-part of continental crust can cover-up oceanic crust. Also, in the places of continental crust; both SiAl and SiMa could be found
Now a geology student is telling me, that is wrong. SiAl is Same as Continental crust, and SiMa is same as Oceanic crust. He's Also telling, "SiAl or Continental crust lie upon Sima or Oceanic crust". That implies at the same-place on Earth, continental and oceanic crust occur together, one upon other.