I believe that the first-ever tie-breaker was a first to 5, sudden death. That was called a 9-point, because the maximum number of points that could be played was 9.
The tie-breaker was modified so it was first-to-seven, and win by two. It was called a 12-point because the score could be 7-5 before going into extra points.
Then the first-to-ten win-by-two came along. Seems to me like it should have been called an 18-point just to carry on the tradition, but someone named it the 10-point to confuse things. Don't know why. Seems like it would be less confusing if they'd rename the 12-point to a 7-point, but doubt that will happen.