Also, if I have a 40 cpl, if there were moves that were better why would they not be an innacuracy?
Average centipawn loss is the difference of your move to the best computer move averaged over all moves.
Inaccuracies/Mistakes/blunders as defined per lichess are moves that are at least 0.5=50 centipawns / 1=100 centipawns / 3=300 centipawns worse than the suggested computer move.
This rule is not strictly enforced in situations where you have a clear winning position and a choice of several good moves.
So if you have a choice between a move that leads to +10 advantage (best computer move) and +9 advantage this will count to your centipawn loss, but will not show up as mistake.
Even without it, it is possible to collect centipawn losses < 50 that don't show up as inaccuracy.