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.