When we see "regression" in fantasy, it& #39;s usually about a player over or underperforming in a stat relative to the league-wide sample (usually over multiple seasons). When a player is way above or below the average of that sample, he& #39;s a positive or negative regression candidate.
It does not mean that every player regresses to the mean of the sample. We have very good reasons to believe some players& #39; true expectation over a big sample would be above or below the league-wide average. For example, we very much should believe Mahomes& #39; TD% is higher than avg.