Good explanation of the phenomenon. Some thoughts:

The first two quotes and your explanations for them are good. But in this part:

"These statements seem contradictory, yet both describe real effects. The apparent contradiction is caused by a phenomenon known as "regression to the mean,""

I would add a sentence stating that positive reinforcement is not the actual cause of the regression. This will end any confusion. Additionally, the example with the IQ test needs a bit more clarification. While the average human IQ is around 100, the kid doesn't necessarily regress to the same average. Most humans have their own "average" that they regress or improve to after periods of extreme positive or negative performance. So the kid might not regress at all if his natural ability is indeed that high.