I suspect that people happened to have just zoned out during this part of the class, although a friend of mine recently said he was never taught that one is suppose to stay as far right as needed to allow people to pass on the left either.
And its not just random drivers, the more esoteric parts of the law (driving on the shoulder in TX, free right turns, uturn laws, center turning lane, etc) aren't even understood by many traffic enforcement officers.
In California, for a single left turn lane, you're allowed to complete the turn into any of the lanes you choose.
The driver handbook doesn't go into detail about double turn lanes that feed into a 3-lane cross street. My own rule is that only the inner lane (leftmost) must complete the turn in the matching innermost lane. The outer lane can end their turn in the #2 or #3 lane. I tend to choose the #3 lane just to put as much space between me and the car next to me, in case they incorrectly go for the #2 lane. Unless there's an opposing right-turning car that I trust less :)