Perhaps your friend was giving the standard Missed procedures given my ATC at a particular airport? I can't see anyone flying anything other than the standard missed procedure in the absence of specific instructions to the contrary. The Jepp charts don't give reasons for a 20 degree turn to the left--maybe there is an obstacle there.
I think what your friend may have been relaying were simply the standard operating procedures that ATC follows at the specific airport that he flew into, and perhaps what speedbird was teaching was what to expect as far as instructions from ATC when going missed.
I don't see any other explanation, as really how can the pilot know why the Missed procedure calls for something different? When is the left turn for traffic management and when is it for obstacle clearance?