When callbacks are enabled, serial port data is collected through some unspecified asynchronous operation.
I believe that the Execution Engine checks whether a callback has been triggered, at the beginning of every line of MATLAB code. (So if you have a tight loop that is coded all on one line, potentially the loop will not get interrupted.)
I believe that serial port callbacks (and timer callbacks) do not need to wait for waitfor() or pause() or drawnow() or figure()
