Your self-defence instructor was, hopefully, stating his preference rather than fact.
Ideally, while self defense shootings take place at close range, they do not involve a struggle for the weapon. While this DOES happen, I decided long ago that if I were involved in an actual physical confrontation, ie a wrasslin' match on the ground, it may be better to NOT draw a weapon.
But I digress. Revolvers are easy to learn, easy to teach, feature the built in safety of a DA first shot with no other safeties or controls, and are, generally, very reliable.
So is my Sig 226, no problems in over 5,000 rounds under all conditions.
It's a matter of preference.
I like autos because they are reliable enough for me, flatter, hold more rounds and are quicker to reload for all but the most skilled operators.