Not trying to bust your chops, but this is not exactly 💯 true, and these vague statements only add to confusion on the topic. (Not to mention this is a 1 year old topic and Cowboy Ted has already progressed to TL).
As was pointed out by several others already, BOP3/BOP5/Custom courses WILL count as ranked rounds in your stats, but WILL NOT count as ranked rounds towards saturation or change your overall average.
So in your example, if he had 2200 when turning TL and played 750 RR his new total of RR in the stats would be 2950 as you say. However, if 5 of those RR were BOP3, 10 were BOP5, and 10 were Custom Courses, those 25 RR would not count towards saturation or average, leaving him 25 short of saturation. Your example would be true in a "perfect world" where no BOP3/BOP5/Customs were played, but that's hard to accomplish in 750 rounds.
Also the required average is 59 or lower, not 58.99. Seems nit-picky but that .01 can take a while to knock out depending on your score history.