I have thought (maybe too much, lol) a lot about this.
"Average centipawn loss (cpl) is the difference of your move to the best computer move averaged over all moves." Yes.
Like all averages this is pretty meaningless without some measure of variance. Very long games will tend to have a smaller cpl because of so many moves and there are not a lot of differences in the value of variations with only a few pieces left on the board. Simply put with lots of moves you are dividing by a larger number, there is little variance between move choices, and this yields a small cpl.
Also, there are games where the top 10 moves will vary in value very little e.g. closed positions like a stonewall. These games will show a low cpl.
I tend to play a very positional game where the positions end up with valuations that vary very little across any of the top 6-8 moves. These games show a low cpl. It does not mean I am playing well. It means the games are intrinsically calm, not sharp and tactical.
So if we had a measure of variance to go along with the cpl we would have a context to better understand what a cpl means. A 25 cpl with a high variance would mean you played rather well. A 25 cpl with a low variance would mean you played OK.